EOSEW / Eos Energy Enterprises, Inc. - Equity Warrant - SEC-arkiveringar, Årsredovisning, Fullmaktsutlåtande

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): June 3, 2026 EOS ENERGY ENTERPRIS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): June 3, 2026 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

Eos Energy Stockholders Approve All Proposals at 2026 Annual Meeting Increased share authorization provides the capital structure flexibility to fund the planned Frontier Power USA Investment EDISON, N.J.— June 5, 2026 — Eos Energy Enterprises, Inc.

annualshareholdermeeting Eos Energy Stockholders Approve All Proposals at 2026 Annual Meeting Increased share authorization provides the capital structure flexibility to fund the planned Frontier Power USA Investment EDISON, N.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD Specialized Disclosure Report EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Commission file number 001-39291

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD Specialized Disclosure Report EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Commission file number 001-39291 Delaware 84-4290188 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification No.) 3920 Park Avenue, Edison, New Jersey 08820 (Address o

EOS ENERGY ENTERPRISES, INC. CONFLICT MINERALS REPORT FOR THE YEAR ENDED DECEMBER 31, 2025

Exhibit 1.01 EOS ENERGY ENTERPRISES, INC. CONFLICT MINERALS REPORT FOR THE YEAR ENDED DECEMBER 31, 2025 Introduction Eos Energy Enterprises, Inc. (“we”, “us”, “our”, the “Company” or “Eos”) is submitting this Conflict Minerals Report (the “Report”) for the calendar year ended December 31, 2025, as required by Rule 13p-1 under the Securities Exchange Act of 1934 (the “Rule”). All terms used but not

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 12, 2026 EOS ENERGY ENTERPRIS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 12, 2026 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

As filed with the Securities and Exchange Commission on May 13, 2026

As filed with the Securities and Exchange Commission on May 13, 2026 Registration No.

Security Type

Calculation of Filing Fee Tables S-3 Eos Energy Enterprises, Inc. Table 1: Newly Registered and Carry Forward Securities ☐Not Applicable Security Type Security Class Title Fee Calculation or Carry Forward Rule Amount Registered Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Carry Forward Form Type Carry Forward File Number Carry Forwar

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2026 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39291 EOS ENERGY ENTERPRISE

Eos Energy Enterprises and Cerberus Capital Management Announce Frontier Power USA to Deploy American-Made Long Duration Energy Storage at Scale Frontier Power USA is expected to be a purpose-built independent development and investment company utili

eosepressreleasefrontier Eos Energy Enterprises and Cerberus Capital Management Announce Frontier Power USA to Deploy American-Made Long Duration Energy Storage at Scale Frontier Power USA is expected to be a purpose-built independent development and investment company utilizing Eos’ vertically integrated technology stack to accelerate gigawatt-scale deployment of American- made energy storage  2 GWh Firm Capacity Reservation Agreement: Eos entered into a 2 GWh Capacity Reservation Agreement securing dedicated manufacturing capacity for Frontier Power USA  ~$1.

Eos Energy Enterprises Reports First Quarter 2026 Financial Results and Announces Frontier Power USA • Announced with Cerberus the formation of Frontier Power USA, a stand-alone purpose-built entity to develop, finance, and operate LDES projects to a

eoseq1fy26earningsreleas Eos Energy Enterprises Reports First Quarter 2026 Financial Results and Announces Frontier Power USA • Announced with Cerberus the formation of Frontier Power USA, a stand-alone purpose-built entity to develop, finance, and operate LDES projects to accelerate energy storage deployments • Entered into a 2 GWh firm capacity reservation agreement with Frontier Power USA • $57.

Employment Agreement This Employment Agreement (this “Agreement”) is dated as of April 28, 2026 (the “Effective Date”), and is made by and between Eos Energy Storage LLC, a Delaware limited liability company, on behalf of itself and its former, prese

a20260428executiveagreem Employment Agreement This Employment Agreement (this “Agreement”) is dated as of April 28, 2026 (the “Effective Date”), and is made by and between Eos Energy Storage LLC, a Delaware limited liability company, on behalf of itself and its former, present, and future parent corporations, stockholders, members, subsidiaries, and affiliates, and each of their respective former, present, and future directors, officers, members, managers, employees, agents, representatives, and insurers, and/or any other related entity (the “Company”) and Alessandro Lagi (“Executive”).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): April 29, 2026 EOS ENERGY ENTERPR

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): April 29, 2026 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commis

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☒ Definitive Proxy State

Eos Ingenuity Lab Research and Development Center Corporate Headquarters 3920 Park Avenue Edison, NJ 08820 United States Eos Ingenuity Park Manufacturing Facilities Manufacturing #1 200 Braddock Ave Turtle Creek, PA 15145 Manufacturing #2 700 Braddoc

ar41426proof Eos Ingenuity Lab Research and Development Center Corporate Headquarters 3920 Park Avenue Edison, NJ 08820 United States Eos Ingenuity Park Manufacturing Facilities Manufacturing #1 200 Braddock Ave Turtle Creek, PA 15145 Manufacturing #2 700 Braddock Ave Turtle Creek, PA 15145 Manufacturing #3 150 Thorn Hill Rd Warrendale, PA 15086 2025 Annual Report Limitless possibilities, across the energy ecosystem.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): April 9, 2026 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): April 9, 2026 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

Eos Energy Enterprises Reports Preliminary Q1 Revenue, Highlights Record Output and Capacity Expansion PITTSBURGH, PA, April 9, 2026 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) ("Eos" or the “Company”), an American energy company and the leading in

q12026businessupdate040 Eos Energy Enterprises Reports Preliminary Q1 Revenue, Highlights Record Output and Capacity Expansion PITTSBURGH, PA, April 9, 2026 — Eos Energy Enterprises, Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 30, 2026 EOS ENERGY ENTERPR

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 30, 2026 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commis

Amended and Restated Employment Agreement

Exhibit 10.1 Amended and Restated Employment Agreement This Amended and Restated Employment Agreement (this “Agreement”) is dated as of March 30, 2026 (the “Effective Date”), and is made by and between Eos Energy Storage LLC, a Delaware limited liability company, on behalf of itself and its former, present, and future parent corporations, stockholders, members, subsidiaries, and affiliates, and ea

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☒ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 24, 2026 EOS ENERGY ENTERPR

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 24, 2026 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commis

Eos Energy Enterprises Appoints Nathaniel Fick to Board of Directors PITTSBURGH, PA, March 26, 2026 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) ("Eos" or the “Company”), an American energy company and the leading innovator in designing, sourcing, m

eospressreleasedirectorn Eos Energy Enterprises Appoints Nathaniel Fick to Board of Directors PITTSBURGH, PA, March 26, 2026 — Eos Energy Enterprises, Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 26, 2026 EOS ENERGY ENTE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 26, 2026 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Com

Execution Version 1 LIMITED CONSENT TO LOAN GUARANTEE AGREEMENT AND AMENDMENT TO ACCOUNTS AGREEMENT This LIMITED CONSENT AND AMENDMENT TO ACCOUNTS AGREEMENT, dated November ___, 2025 (this “Limited Consent”), between the UNITED STATES DEPARTMENT OF E

eos-doelimitedconsenttol Execution Version 1 LIMITED CONSENT TO LOAN GUARANTEE AGREEMENT AND AMENDMENT TO ACCOUNTS AGREEMENT This LIMITED CONSENT AND AMENDMENT TO ACCOUNTS AGREEMENT, dated November , 2025 (this “Limited Consent”), between the UNITED STATES DEPARTMENT OF ENERGY, an agency of the United States of America (“DOE”), EOS ENERGY ENTERPRISES, INC.

Eos Energy Enterprises Reports Fourth Quarter and Full Year 2025 Financial Results; Delivers More than 7x Year-Over-Year Revenue Growth and Initiates 2026 Revenue Guidance • $58.0 million in record quarterly revenue with Q4 exceeding the first three

eoseq4fy25earningsreleas Eos Energy Enterprises Reports Fourth Quarter and Full Year 2025 Financial Results; Delivers More than 7x Year-Over-Year Revenue Growth and Initiates 2026 Revenue Guidance • $58.

EX-10.44

lgaamendment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended: December 31, 2025 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 EOS ENERGY ENTERPRISES, INC. Delaware 001-39291 84-4290188 (State or other jurisdiction of inco

#9857019 v3 \027606 \0008 INSIDER TRADING POLICY Revised and adopted by the Board of Directors on March 13, 2023 TRADING IN COMPANY SECURITIES WHILE IN POSSESSION OF MATERIAL NONPUBLIC INFORMATION IS PROHIBITED The purchase or sale of securities by a

insidertradingpolicy #9857019 v3 \027606 \0008 INSIDER TRADING POLICY Revised and adopted by the Board of Directors on March 13, 2023 TRADING IN COMPANY SECURITIES WHILE IN POSSESSION OF MATERIAL NONPUBLIC INFORMATION IS PROHIBITED The purchase or sale of securities by any person who possesses material nonpublic information is a violation of federal and state securities laws.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 13, 2026 EOS ENERGY ENTE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 13, 2026 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Com

Execution Version 1 SECOND AMENDMENT TO LOAN GUARANTEE AGREEMENT This SECOND AMENDMENT TO LOAN GUARANTEE AGREEMENT, dated February 13, 2026 (this "Amendment"), is made by and between the UNITED STATES DEPARTMENT OF ENERGY, an agency of the United Sta

doe-secondamendmenttolga Execution Version 1 SECOND AMENDMENT TO LOAN GUARANTEE AGREEMENT This SECOND AMENDMENT TO LOAN GUARANTEE AGREEMENT, dated February 13, 2026 (this "Amendment"), is made by and between the UNITED STATES DEPARTMENT OF ENERGY, an agency of the United States of America ("DOE") and EOS ENERGY ENTERPRISES, INC.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): December 22, 2025 EOS ENERGY ENTE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): December 22, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Com

Eos Energy Honors Outgoing Chair Russ Stidolph for Years of Leadership and Investment and Appoints Industry Veteran Joseph Nigro as Chair of the Board of Directors EDISON, N.J., Dec. 22, 2025 – Eos Energy Enterprises, Inc. (NASDAQ: EOSE) ("Eos" or th

pressreleasedirector-122 Eos Energy Honors Outgoing Chair Russ Stidolph for Years of Leadership and Investment and Appoints Industry Veteran Joseph Nigro as Chair of the Board of Directors EDISON, N.

SIXTH AMENDMENT to CREDIT AND GUARANTY AGREEMENT

Exhibit 10.1 SIXTH AMENDMENT to CREDIT AND GUARANTY AGREEMENT This SIXTH AMENDMENT to CREDIT AND GUARANTY AGREEMENT (this “Agreement”) is made as of November 19, 2025, by and among EOS ENERGY ENTERPRISES, INC., a Delaware corporation, as borrower (the “Borrower”) and grantor, the guarantors and other grantors party hereto, the Lenders party hereto, and CERBERUS US SERVICING, LLC, as Administrative

Eos Energy Enterprises, Inc. WILMINGTON TRUST, NATIONAL ASSOCIATION as Trustee Dated as of November 24, 2025 1.75% Convertible Senior Notes due 2031 TABLE OF CONTENTS

Exhibit 4.1 EXECUTION VERSION Eos Energy Enterprises, Inc. and WILMINGTON TRUST, NATIONAL ASSOCIATION as Trustee INDENTURE Dated as of November 24, 2025 1.75% Convertible Senior Notes due 2031 TABLE OF CONTENTS Page Article 1. Definitions; Rules of Construction 1 Section 1.01. Definitions 1 Section 1.02. Other Definitions 13 Section 1.03. Rules of Construction 14 Article 2. The Notes 15 Section 2.

Eos Energy Enterprises, Inc. Announces Proposed Convertible Senior Notes Offering

Exhibit 99.1 Eos Energy Enterprises, Inc. Announces Proposed Convertible Senior Notes Offering EDISON, N.J., Nov. 18, 2025 (GLOBE NEWSWIRE)—Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”) today announced its intention to offer, subject to market and other conditions, $500,000,000 aggregate principal amount of convertible senior notes due 2031 (the “notes”) in a private offerin

FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of Earliest Event Reported): November 18, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter)

FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of Earliest Event Reported): November 18, 2025 EOS ENERGY ENTERPRISES, INC.

Eos Energy Enterprises, Inc. Prices Upsized $525,000,000 Convertible Senior Notes Offering

Exhibit 99.2 Eos Energy Enterprises, Inc. Prices Upsized $525,000,000 Convertible Senior Notes Offering EDISON, N.J., Nov. 20, 2025 (GLOBE NEWSWIRE)—Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”) today announced the pricing of its offering of $525,000,000 aggregate principal amount of 1.75% convertible senior notes due 2031 (the “notes”) in a private offering (the “Offering”)

35,855,647 Shares Eos Energy Enterprises, Inc. Common Stock

Filed Pursuant to Rule 424(b)(5) Registration No. 333-287629 Prospectus Supplement (To Prospectus dated May 29, 2025) 35,855,647 Shares Eos Energy Enterprises, Inc. Common Stock We are offering 35,855,647 shares of our common stock, par value $0.0001 per share, in a registered direct offering to a limited number of purchasers pursuant to this prospectus supplement and the accompanying prospectus a

PRICING TERM SHEET November 19, 2025 Eos Energy Enterprises, Inc. 35,855,647 shares of Common Stock

Issuer Free Writing Prospectus Filed Pursuant to Rule 433 Registration Statement No.

FIFTH AMENDMENT to CREDIT AND GUARANTY AGREEMENT

Exhibit 10.1 Execution Version FIFTH AMENDMENT to CREDIT AND GUARANTY AGREEMENT This FIFTH AMENDMENT to CREDIT AND GUARANTY AGREEMENT (this “Agreement”) is made as of November 18, 2025, by and among EOS ENERGY ENTERPRISES, INC., a Delaware corporation, as borrower (the “Borrower”) and grantor, the guarantors and other grantors party hereto, the Lenders party hereto, and CERBERUS US SERVICING, LLC,

WARRANT AGREEMENT

Exhibit 10.2 Execution Version WARRANT AGREEMENT WARRANT AGREEMENT dated as of November 18, 2025 (this “Agreement”), between EOS ENERGY ENTERPRISES, INC., a corporation organized under the laws of Delaware (the “Company”) and the U.S. Department of Energy (“Guarantor”). WHEREAS, the Company and the Guarantor are parties to a Loan Guarantee Agreement, dated November 26, 2024 (the “Loan Guarantee Ag

SUBJECT TO COMPLETION, DATED NOVEMBER 18, 2025

The information in this preliminary prospectus supplement is not complete and may be changed.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 18, 2025 EOS ENERGY ENTE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 18, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Com

Eos Energy Enterprises Delivers Highest Company Quarterly Revenue, Doubling Second Quarter 2025, and Reports Third Quarter 2025 Financial Results Reaffirms full year revenue guidance in the range of $150 to $160 million consistent with the low end of

eoseq32025earningsreleas Eos Energy Enterprises Delivers Highest Company Quarterly Revenue, Doubling Second Quarter 2025, and Reports Third Quarter 2025 Financial Results Reaffirms full year revenue guidance in the range of $150 to $160 million consistent with the low end of the Company’s forecasted range • $30.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39291 EOS ENERGY ENTERP

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 5, 2025 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 5, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): October 31, 2025 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): October 31, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

Eos Energy Secures Strategic 228 MWh Order from Frontier Power Under Existing 5 GWh Framework Agreement & Achieves Final Cerberus Milestone Order strengthens growing partnership to deploy long-duration energy storage across multiple markets PITTSBURG

pressreleasefrontiervf Eos Energy Secures Strategic 228 MWh Order from Frontier Power Under Existing 5 GWh Framework Agreement & Achieves Final Cerberus Milestone Order strengthens growing partnership to deploy long-duration energy storage across multiple markets PITTSBURGH, P.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): October 16, 2025 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): October 16, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

Security Type

Calculation of Filing Fee Tables S-3 Eos Energy Enterprises, Inc. Table 1: Newly Registered and Carry Forward Securities ☐Not Applicable Security Type Security Class Title Fee Calculation or Carry Forward Rule Amount Registered Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Carry Forward Form Type Carry Forward File Number Carry Forwar

As filed with the Securities and Exchange Commission on October 2, 2025

As filed with the Securities and Exchange Commission on October 2, 2025 Registration No.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. )

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. ) Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Defin

144

144 0001991521 XXXXXXXX LIVE 0001805077 Eos Energy Enterprises, Inc. 001-39291 3920 PARK AVENUE EDISON NJ 08820 (732) 225-8400 Puri Sumeet Officer Common UBS Financial Services Inc. 11 Madison Avenue 4th Floor New York NY 10010 20501 143006.78 259853606 09/08/2025 Nasdaq Common UBS Fincial Services Inc. 11 Madison Ave 4th Floor New York NY 10010 20000 145062.00 259853606 09/08/2025 Nasdaq Common 0

144

144 0001782905 XXXXXXXX LIVE 0001805077 Eos Energy Enterprises, Inc. 001-39291 3920 Park Avenue Edison NJ 08820 7322258400 Marian Walters Officer Common UBS Financial Services Inc 1000 Harbor Blvd 3rd Floor Weehawken NJ 07086 50000 395091 259853606 09/03/2025 Nasdaq Common 06/15/2021 RSU Vesting Issuer N 5198 06/15/2021 N/A Common 05/15/2023 RSU Vesting Issuer N 10600 05/15/2023 N/A Common 05/14/2

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. )

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. ) Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Defin

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☒ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☒ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

between the Company and W

4926-1326-4467 v.12 FIRST SUPPLEMENTAL INDENTURE Dated as of July 28, 2025 between EOS ENERGY ENTERPRISES, INC. as Company and WILMINGTON TRUST, NATIONAL ASSOCIATION, as Trustee to the Indenture dated as of May 25, 2023 between the Company and the Trustee 4926-1326-4467 v.12 THIS FIRST SUPPLEMENTAL INDENTURE, dated as of July 28, 2025 (this “Supplemental Indenture”), between Eos Energy Enterprises

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39291 EOS ENERGY ENTERPRISES

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 30, 2025 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 30, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

Fourth Amendment to Credit and Guaranty Agreement, dated July

4901-5195-9128 v.2 CERTAIN INFORMATION IN THIS EXHIBIT MARKED [*] HAS BEEN EXCLUDED FROM THIS EXHIBIT BECAUSE IT IS BOTH (A) NOT MATERIAL AND (B) WOULD BE COMPETITIVELY HARMFUL IF PUBLICLY DISCLOSED FOURTH AMENDMENT TO CREDIT AND GUARANTY AGREEMENT This FOURTH AMENDMENT TO CREDIT AND GUARANTY AGREEMENT (this “Agreement”) is made as of July 29, 2025, by and among EOS ENERGY ENTERPRISES, INC., a Del

Eos Energy Enterprises Delivers Record Quarterly Revenue Nearly Equivalent to Full Year 2024, Reports Second Quarter 2025 Financial Results and Reaffirms 2025 Revenue Outlook • $15.2 million revenue, highest in Company history and nearly equivalent t

eoseq22025earningsreleas Eos Energy Enterprises Delivers Record Quarterly Revenue Nearly Equivalent to Full Year 2024, Reports Second Quarter 2025 Financial Results and Reaffirms 2025 Revenue Outlook • $15.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 23, 2025 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 23, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 1, 2025 EOS ENERGY ENTERPRIS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 1, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

Eos Energy Announces Second Funding Under its Department of Energy Loan Guarantee to Fuel U.S. Battery Manufacturing Capacity Expansion $22.7 million second loan advance follows the first $68.3 million received in December 2024 TURTLE CREEK, Pa., Jul

Eos Energy Announces Second Funding Under its Department of Energy Loan Guarantee to Fuel U.

Calculation of Filing Fee Table

EXHIBIT 107 Calculation of Filing Fee Table Form S-8 (Form Type) Eos Energy Enterprises, Inc.

First Amendment to the Second Amended and Restated 2020 Incentive Plan

First Amendment to the Eos Energy Enterprises, Inc. Second Amended and Restated 2020 Incentive Plan This First Amendment (this “Amendment”) to the Eos Energy Enterprises, Inc. Second Amended and Restated 2020 Incentive Plan (as amended, restated, replaced, supplemented, or otherwise modified from time to time, the “Plan”) is approved and adopted to be effective as of May 15, 2025 (the “Effective D

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter)

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 3690 84-4290188 (State or other jurisdiction of incorporation) (Primary Standard Industrial Classification Code Number) (IRS Employer Identification No.) 3920 Park Avenue

Entry into a Material Definitive Agreement, Unregistered Sales of Equity Securities, Financial Statements and Exhibits, Triggering Events That Accelerate or Increase a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement, Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant, Other Events

FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of Earliest Event Reported): May 29, 2025 EOS ENERGY ENTERPRISES, INC.

Indenture, dated as of June 3, 2025, between Eos Energy Enterprises, Inc. and Wilmington Trust, National Association, as trustee

Exhibit 4.1 EXECUTION VERSION Eos Energy Enterprises, Inc. and WILMINGTON TRUST, NATIONAL ASSOCIATION as Trustee INDENTURE Dated as of June 3, 2025 6.75% Convertible Senior Notes due 2030 TABLE OF CONTENTS Page Article 1. Definitions; Rules of Construction 1 Section 1.01. Definitions. 1 Section 1.02. Other Definitions. 13 Section 1.03. Rules of Construction. 14 Article 2. The Notes 15 Section 2.01

Eos Energy Enterprises, Inc. Prices Upsized $225,000,000 Convertible Senior Notes Offering

Exhibit 99.2 Eos Energy Enterprises, Inc. Prices Upsized $225,000,000 Convertible Senior Notes Offering EDISON, N.J., May 30, 2025 (GLOBE NEWSWIRE)—Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”) today announced the pricing of its offering of $225,000,000 aggregate principal amount of 6.75% convertible senior notes due 2030 (the “notes”) in a private offering to persons reason

Eos Energy Enterprises, Inc. Announces Proposed Convertible Senior Notes Offering

Exhibit 99.1 Eos Energy Enterprises, Inc. Announces Proposed Convertible Senior Notes Offering EDISON, N.J., May 29, 2025 (GLOBE NEWSWIRE)—Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”) today announced its intention to offer, subject to market and other conditions, $175,000,000 aggregate principal amount of convertible senior notes due 2030 (the “notes”) in a private offering

Eos Energy Enterprises, Inc. Conflict Minerals Report - December 31, 202

Exhibit 1.01 EOS ENERGY ENTERPRISES, INC. CONFLICT MINERALS REPORT FOR THE YEAR ENDED DECEMBER 31, 2024 Introduction Eos Energy Enterprises, Inc. (“we”, “us”, “our”, the “Company” or “Eos”) is submitting this Conflict Minerals Report (the “Report”) for the calendar year ended December 31, 2024, as required by Rule 13p-1 under the Securities Exchange Act of 1934 (the “Rule”). All terms used but not

18,750,000 Shares Eos Energy Enterprises, Inc. Common Stock

Filed Pursuant to Rule 424(b)(5) Registration No. 333-287629 Prospectus Supplement (To Prospectus dated May 29, 2025) 18,750,000 Shares Eos Energy Enterprises, Inc. Common Stock This is a public offering of common stock of Eos Energy Enterprises, Inc. We are offering all of the shares of common stock to be sold in the offering. Our common stock is listed on the Nasdaq Capital Market (“Nasdaq”) und

Underwriting Agreement, dated as of May 29, 2025, between Eos Energy Enterprises, Inc. and J.P. Morgan Securities LLC and Jefferies LLC.

Exhibit 1.1 Eos Energy Enterprises, Inc. 18,750,000 Shares of Common Stock Underwriting Agreement May 29, 2025 J.P. Morgan Securities LLC Jefferies LLC As Representatives of the several Underwriters listed in Schedule 1 hereto c/o J.P. Morgan Securities LLC 383 Madison Avenue New York, New York 10179 c/o Jefferies LLC 520 Madison Avenue New York, New York 10022 Ladies and Gentlemen: Eos Energy Ent

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of Earliest Event Reported): May 28, 2025 EOS ENERGY ENTERPRIS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of Earliest Event Reported): May 28, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

Third Amendment to Credit and Guaranty Agreement, dated May 29, 2025, by and among the Company, CCM Denali Debt Holdings, LP and Cerberus US Servicing, LLC

Exhibit 10.1 THIRD AMENDMENT to CREDIT AND GUARANTY AGREEMENT This THIRD AMENDMENT to CREDIT AND GUARANTY AGREEMENT (this “Agreement”) is made as of May 30, 2025, by and among EOS ENERGY ENTERPRISES, INC., a Delaware corporation, as borrower (the “Borrower”) and grantor, the guarantors and other grantors party hereto, the Lenders party hereto, and CERBERUS US SERVICING, LLC, as Administrative Agen

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD Specialized Disclosure Report EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Commission file number 001-39291

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD Specialized Disclosure Report EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Commission file number 001-39291 Delaware 84-4290188 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification No.) 3920 Park Avenue, Edison, New Jersey 08820 (Address o

Calculation of Filing Fee Tables FORM 424(b)(5) (Form Type) Eos Energy Enterprises, Inc. (Exact Name of Registrant as Specified in its Articles of Association) Table 1: Newly Registered and Carry Forward Securities

Exhibit 107 Calculation of Filing Fee Tables FORM 424(b)(5) (Form Type) Eos Energy Enterprises, Inc.

PRICING TERM SHEET May 29, 2025 Eos Energy Enterprises, Inc. Offering of 18,750,000 shares of Common Stock

Issuer Free Writing Prospectus Filed Pursuant to Rule 433 Registration Statement No.

LIMITED WAIVER

Exhibit 99.1 Execution Version LIMITED WAIVER This LIMITED WAIVER (this “Agreement”) is made as of May 28, 2025, by and among Eos Energy Enterprises, Inc., a Delaware corporation (the “Company”) and CCM Denali Equity Holdings, LP (the “Purchaser”). RECITALS WHEREAS, the Company and Purchaser are parties to that certain Securities Purchase Agreement, dated June 21, 2024 (the “Securities Purchase Ag

As filed with the Securities and Exchange Commission on May 29, 2025

As filed with the Securities and Exchange Commission on May 29, 2025 Registration No.

Limited Consent to Loan Guarantee Agreement, dated May 28, 2025, by and between the Company and the United States Department of Energy

Exhibit 10.2 Execution Version LIMITED CONSENT TO LOAN GUARANTEE AGREEMENT This LIMITED CONSENT, dated May 28, 2025 (this “Limited Consent”), between the UNITED STATES DEPARTMENT OF ENERGY, an agency of the United States of America (“DOE”) and EOS ENERGY ENTERPRISES, INC., a corporation organized and existing under the laws of the State of Delaware (the “Borrower” and together with DOE, each a “Pa

SUBJECT TO COMPLETION, DATED MAY 29, 2025

The information in this preliminary prospectus supplement is not complete and may be changed.

Filing Fee Table

Exhibit 107 Calculation of Filing Fee Tables Form S-3 (Form Type) Eos Energy Enterprises, Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 29, 2025 EOS ENERGY ENTERPRIS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 29, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

Second Amendment to Credit and Guaranty Agreement, dated May 28, 2025, by and among the Company, CCM Denali Debt Holdings, LP and Cerberus US Servicing, LLC

Exhibit 10.1 Execution Version SECOND AMENDMENT to CREDIT AND GUARANTY AGREEMENT This SECOND AMENDMENT to CREDIT AND GUARANTY AGREEMENT (this “Agreement”) is made as of May 28, 2025, by and among EOS ENERGY ENTERPRISES, INC., a Delaware corporation, as borrower (the “Borrower”) and grantor, the guarantors and other grantors party hereto, the Lenders party hereto, and CERBERUS US SERVICING, LLC, as

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 27, 2025 EOS ENERGY ENTERPRIS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 27, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

Financial Statements and Exhibits, Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 15, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

May 9, 2025

May 9, 2025 VIA EDGAR Division of Corporation Finance Securities & Exchange Commission 100 F Street, N.

As filed with the Securities and Exchange Commission on May 7, 2025

As filed with the Securities and Exchange Commission on May 7, 2025 Registration No.

Filing Fee Table

Exhibit 107 Calculation of Filing Fee Table Registration Statement on Form S-3 (Form Type) EOS ENERGY ENTERPRISES, INC.

As filed with the Securities and Exchange Commission on May 7, 2025

As filed with the Securities and Exchange Commission on May 7, 2025 Registration No.

Filing Fee Table

Exhibit 107 Calculation of Filing Fee Table Registration Statement on Form S-3 (Form Type) EOS ENERGY ENTERPRISES, INC.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39291 EOS ENERGY ENTERPRISE

Eos Energy Enterprises Records Highest Quarterly Revenue and Reports First Quarter 2025 Financial Results and Reaffirms 2025 Outlook • $10.5 million quarterly revenue, highest in Company history as production ramps to deliver customer backlog • Year-

Eos Energy Enterprises Records Highest Quarterly Revenue and Reports First Quarter 2025 Financial Results and Reaffirms 2025 Outlook • $10.

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 6, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissio

First Amendment to Credit and Guaranty Agreement, dated April 30, 2025, by and between Eos Energy Enterprises, Inc. and Cerberus US Servicing, LLC

4907-2962-2537 v.5 CERTAIN INFORMATION IN THIS EXHIBIT MARKED [*] HAS BEEN EXCLUDED FROM THIS EXHIBIT BECAUSE IT IS BOTH (A) NOT MATERIAL AND (B) WOULD BE COMPETITIVELY HARMFUL IF PUBLICLY DISCLOSED FIRST AMENDMENT TO CREDIT AND GUARANTY AGREEMENT This FIRST AMENDMENT TO CREDIT AND GUARANTY AGREEMENT (this “Agreement”) is made as of April 30, 2025 (the “Amendment Effective Date”), by and among EOS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. )

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No. ) Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Defin

EOS ENERGY ENTERPRISES, INC 2024 ANNUAL REPORT 2024 Annual Shareholder Letter A Message from Joe Mastrangelo, Chief Executive Officer Dear Fellow Shareholders, In 2024, Eos achieved significant operational milestones positioning the company for futur

EOS ENERGY ENTERPRISES, INC 2024 ANNUAL REPORT 2024 Annual Shareholder Letter A Message from Joe Mastrangelo, Chief Executive Officer Dear Fellow Shareholders, In 2024, Eos achieved significant operational milestones positioning the company for future success.

Joseph Nigro Appointed to Eos Energy Enterprises Board of Directors Nigro brings decades of leadership experience in the energy and utility sectors, providing invaluable expertise to drive Eos’ growth and enhance its competitive positioning in the in

Joseph Nigro Appointed to Eos Energy Enterprises Board of Directors Nigro brings decades of leadership experience in the energy and utility sectors, providing invaluable expertise to drive Eos’ growth and enhance its competitive positioning in the industry EDISON, N.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☒ Definitive Proxy State

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 26, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commis

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 2, 2025 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 2, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

Offer Letter, dated March 3, 2025, by and between the Company and Eric Javidi

1 Eos Energy Storage LLC 3920 Park Avenue Edison, NJ 08820 (732) 225-8400 www.eose.com March 3, 2025 DELIVERED VIA EMAIL Mr. Eric Javidi RE: Offer of Employment Dear Eric: We are pleased to extend to you this conditional offer of employment (this "Offer Letter") with Eos Energy Storage LLC, a Delaware limited liability company (the "Company"), subject to the completion of certain pre- employment r

Eos Energy Enterprises, Inc. Short-Term Incentive Compensation Plan

Page 1 Eos Energy Enterprises, Inc. Short-Term Incentive Compensation Plan (Effective as of March 2, 2025) 1. Establishment of the Plan: The Board of Directors (the “Board”) of Eos Energy Enterprises, Inc., a Delaware corporation (“Eos”), hereby establishes a short-term incentive compensation plan for Eos and its Subsidiaries (collectively, the “Company”) to be known as the “Short-Term Incentive C

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 4, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

sider Trading Policy

insidertradingpolicy #9857019 v3 \027606 \0008 INSIDER TRADING POLICY Revised and adopted by the Board of Directors on March 13, 2023 TRADING IN COMPANY SECURITIES WHILE IN POSSESSION OF MATERIAL NONPUBLIC INFORMATION IS PROHIBITED The purchase or sale of securities by any person who possesses material nonpublic information is a violation of federal and state securities laws.

Eos Energy Enterprises Meets 2024 Revised Revenue Guidance and Reports Fourth Quarter & Full-Year 2024 Financial Results; Reaffirms 2025 Revenue Guidance • Achieved Cerberus third tranche of operational performance milestones and secured final $40.5

Eos Energy Enterprises Meets 2024 Revised Revenue Guidance and Reports Fourth Quarter & Full-Year 2024 Financial Results; Reaffirms 2025 Revenue Guidance • Achieved Cerberus third tranche of operational performance milestones and secured final $40.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended: December 31, 2024 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 EOS ENERGY ENTERPRISES, INC. Delaware 001-39291 84-4290188 (State or other jurisdiction of inco

Certificate of Designation of Series B-4 Non-Voting Convertible Preferred Stock.

Exhibit 3.1 CERTIFICATE OF DESIGNATION OF SERIES B-4 NON-VOTING CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of the State of Delawar

Eos Energy Secures Cerberus Delayed Draw Term Loan Full Funding, Continuing U.S. Manufacturing Capacity to Strengthen America’s Energy Independence

Exhibit 99.1 Eos Energy Secures Cerberus Delayed Draw Term Loan Full Funding, Continuing U.S. Manufacturing Capacity to Strengthen America’s Energy Independence Successfully achieves all operational milestones that guarantees final $40.5 million under $210.5 million Term Loan to further solidify its position as a leader in American energy storage systems. TURTLE CREEK, Pa., January 27, 2025 — Eos

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 24, 2025 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 24, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 16, 2025 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 16, 2025 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

Eos Energy Achieves Full-Year 2024 Revised Revenue Guidance and Provides 2025 Revenue Outlook of at Least 10x Full-Year 2024 EDISON, N.J. – Jan. 16, 2025 - Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”), America’s leading innova

eoseearningspreannouncem Eos Energy Achieves Full-Year 2024 Revised Revenue Guidance and Provides 2025 Revenue Outlook of at Least 10x Full-Year 2024 EDISON, N.

Eos Energy Announces $68.3 Million First Funding from its $303.5 Million Department of Energy Loan Guarantee First Title 17 battery loan guarantee to be funded under the current administration after an application and approval process that began in J

Exhibit 99.2 Eos Energy Announces $68.3 Million First Funding from its $303.5 Million Department of Energy Loan Guarantee First Title 17 battery loan guarantee to be funded under the current administration after an application and approval process that began in January 2021 TURTLE CREEK, PA., Dec. 19, 2024 – Eos Energy Enterprises, Inc. (NASDAQ: EOSE) ("Eos" or the “Company”), America’s leading in

David Urban Appointed to Eos Energy Enterprises Board of Directors Urban brings unparalleled expertise in linking business strategy to public policy enabling Eos to strengthen its position in made in America energy storage systems

Exhibit 99.1 David Urban Appointed to Eos Energy Enterprises Board of Directors Urban brings unparalleled expertise in linking business strategy to public policy enabling Eos to strengthen its position in made in America energy storage systems EDISON, N.J., Dec. 17, 2024 – Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”), America’s leading innovator in the design, sourcing, and

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): December 16, 2024 EOS ENERGY ENTE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): December 16, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Com

EOSE / Eos Energy Enterprises, Inc. / Cerberus Capital Management II, L.P. Activist Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D Under the Securities Exchange Act of 1934 (Amendment No. 5)* EOS ENERGY ENTERPRISES, INC. (Name of Issuer) Common Stock, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) Cerberus Capital Management II, L.P. 875 Third Avenue, 11th Floor New York, NY 10022 (212) 891-2100 Attn: Alex

Eos Energy Closes $303.5 Million Loan Guaranteed by the U.S. Department of Energy to Support Project AMAZE and American Made Manufacturing Expansion Loan supports next phase of Company’s growth, expected to bring annual production capacity to 8 GWh,

Exhibit 99.1 Eos Energy Closes $303.5 Million Loan Guaranteed by the U.S. Department of Energy to Support Project AMAZE and American Made Manufacturing Expansion Loan supports next phase of Company’s growth, expected to bring annual production capacity to 8 GWh, meeting long duration battery energy storage systems’ growing demand First Title 17 Battery loan closed under the current administration

Note Purchase Agreement, dated November 26, 2024, by and among Eos Energy Enterprises, Inc., the U.S. Department of Energy and the Federal Financing Bank

Exhibit 10.1 DOE (Title XVII) EOS ENERGY ENTERPRISES, INC. NOTE PURCHASE AGREEMENT made as of November 26, 2024, by and among the FEDERAL FINANCING BANK (“FFB”), a body corporate and instrumentality of the United States of America, EOS ENERGY ENTERPRISES, INC. (the “Borrower”), a corporation duly organized and existing under the laws of the State of Delaware, and the SECRETARY OF ENERGY, acting th

Future Advance Promissory Note of Eos Energy Enterprises, Inc., dated November 26, 2024

Exhibit 10.2 DOE (Title XVII) EOS ENERGY ENTERPRISES, INC. FOR FFB USE ONLY Note Identifier: EOSENERG 0001 Purchase Date: November 26, 2024 Note Date November 26, 2024 Place of Issue East Pittsburgh, PA Last Day for an Advance (3) December 31, 2027 Maximum Principal Amount (4) $277,497,000 Maturity Date (5) June 15, 2034 Payment Dates (7) March 15, June 15, September 15 & December 15 of each year

Loan Guarantee Agreement, dated November 26, 2024, by and between Eos Energy Enterprises, Inc. and the U.S. Department of Energy

Exhibit 10.3 Execution Version CERTAIN INFORMATION IN THIS EXHIBIT MARKED [*] HAS BEEN EXCLUDED FROM THIS EXHIBIT BECAUSE IT IS BOTH (A) NOT MATERIAL AND (B) THE TYPE OF INFORMATION THAT THE COMPANY CUSTOMARILY AND ACTUALLY TREATS AS PRIVATE AND CONFIDENTIAL. LOAN GUARANTEE AGREEMENT dated as of November 26, 2024 among EOS ENERGY ENTERPRISES, INC., as Borrower, and U.S. DEPARTMENT OF ENERGY, as Gu

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 26, 2024 EOS ENERGY ENTE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 26, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Com

Amendment to Credit Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and Cerberus Capital Management L.P.

Exhibit 10.4 CERTAIN INFORMATION IN THIS EXHIBIT MARKED [*] HAS BEEN EXCLUDED FROM THIS EXHIBIT BECAUSE IT IS BOTH (A) NOT MATERIAL AND (B) THE TYPE OF INFORMATION THAT THE COMPANY CUSTOMARILY AND ACTUALLY TREATS AS PRIVATE AND CONFIDENTIAL. FIRST OMNIBUS AMENDMENT TO CREDIT DOCUMENTS This FIRST OMNIBUS AMENDMENT to CREDIT DOCUMENTS (this “Agreement”) is made as of November 26, 2024 (the “First Am

Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 8, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39291 EOS ENERGY ENTERP

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 5, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

Eos Energy Enterprises Reports Third Quarter 2024 Financial Results and Updates 2024 Outlook • Achieved Cerberus second tranche performance milestones; received incremental $65 million, providing essential capital to serve growing BESS demand • Annou

Eos Energy Enterprises Reports Third Quarter 2024 Financial Results and Updates 2024 Outlook • Achieved Cerberus second tranche performance milestones; received incremental $65 million, providing essential capital to serve growing BESS demand • Announced a 216 MWh purchase order with City Utilities of Springfield, Missouri, Eos’ largest municipal community owned order to date; shipments expected t

EOSE / Eos Energy Enterprises, Inc. / Cerberus Capital Management II, L.P. Activist Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D Under the Securities Exchange Act of 1934 (Amendment No. 4)* EOS ENERGY ENTERPRISES, INC. (Name of Issuer) Common Stock, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) Cerberus Capital Management II, L.P. 875 Third Avenue, 11th Floor New York, NY 10022 (212) 891-2100 Attn: Alex

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): October 31, 2024 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): October 31, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

Certificate of Designation of Series B-3 Non-Voting Convertible Preferred Stock.

Exhibit 3.1 Execution Version CERTIFICATE OF DESIGNATION OF SERIES B-3 NON-VOTING CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of th

Eos Energy Achieves Second Set of Performance Milestones Related to Cerberus Strategic Investment

Exhibit 99.1 Eos Energy Achieves Second Set of Performance Milestones Related to Cerberus Strategic Investment TURTLE CREEK, Pa., October 31, 2024 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”), a leading provider of safe, scalable, efficient, and sustainable zinc-based long duration energy storage systems, today announced the successful achievement of all four of the secon

Certificate of Designation of Series B-1 Non-Voting Convertible Preferred Stock.

Exhibit 3.1 CERTIFICATE OF DESIGNATION OF SERIES B-1 NON-VOTING CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of the State of Delawar

Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year, Financial Statements and Exhibits, Unregistered Sales of Equity Securities, Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): September 10, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Co

Certificate of Designation of Series B-2 Non-Voting Convertible Preferred Stock.

Exhibit 3.2 CERTIFICATE OF DESIGNATION OF SERIES B-2 NON-VOTING CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of the State of Delawar

EOSE / Eos Energy Enterprises, Inc. / Cerberus Capital Management II, L.P. Activist Investment

SC 13D/A 1 formsc13da-eos.htm UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D Under the Securities Exchange Act of 1934 (Amendment No. 3)* EOS ENERGY ENTERPRISES, INC. (Name of Issuer) Common Stock, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) Cerberus Capital Management II, L.P. 875 Third Avenue, 11th Floor New York, NY 1

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

EOSE / Eos Energy Enterprises, Inc. / Cerberus Capital Management II, L.P. Activist Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D Under the Securities Exchange Act of 1934 (Amendment No. 2)* EOS ENERGY ENTERPRISES, INC. (Name of Issuer) Common Stock, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) Cerberus Capital Management II, L.P. 875 Third Avenue, 11th Floor New York, NY 10022 (212) 891-2100 Attn: Alex

2

Exhibit 99.1 Eos Energy Achieves First Performance Milestones Related to Cerberus Strategic Investment $30 million tranche further strengthens the Company’s balance sheet as Eos expands manufacturing operations in Turtle Creek TURTLE CREEK, Pa., August 29, 2024 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”), a leading provider of safe, scalable, efficient, and sustainable z

Series A-2 Preferred Stock Certificate of Designation.

Exhibit 3.1 CERTIFICATE OF DESIGNATION OF SERIES A-2 NON-VOTING NON-CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of the State of Del

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 29, 2024 EOS ENERGY ENTERP

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 29, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commi

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☒ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 6, 2024 EOS ENERGY ENTERPR

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 6, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commis

-Based Restricted Stock Unit Award Agreement

Page 1 EOS ENERGY ENTERPRISES, INC. Restricted Stock Unit Award Agreement (Performance-Based) This Restricted Stock Unit Award Agreement (Performance-Based) (this “Agreement”), dated as of [] [], 20[], is entered into by and between Eos Energy Enterprises, Inc., a Delaware corporation (the “Company”), and the Participant whose name appears on the signature page to this Agreement (the “Participant”

Form of Employee Restricted Stock Unit Award Agreement under the Eos Energy Enterprises, Inc. 2020 Incentive Plan

RESTRICTED STOCK UNIT AWARD AGREEMENT This Restricted Stock Unit Award Agreement (this “Agreement”) is dated as of [Grant Date:Month DD, YYYY], and is made by and between Eos Energy Enterprises, Inc.

Form of Director Optio

DIRECTOR FORM OPTION AWARD AGREEMENT This Option Award Agreement (this “Agreement”) is dated as of [Grant Date:Month DD, YYYY], and is made by and between Eos Energy Enterprises, Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 6, 2024 EOS ENERGY ENTERPR

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 6, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commis

Form of Executive Restricted Stock Unit Award Agreement under the Eos Energy Enterprises, Inc. 2020 Incentive Plan

RESTRICTED STOCK UNIT AWARD AGREEMENT This Restricted Stock Unit Award Agreement (this “Agreement”) is dated effective as of , 202, and is made by and between Eos Energy Enterprises, Inc.

Amended and Restated 2020 Incentive Plan

Page 1 EOS ENERGY ENTERPRISES, INC. Restricted Stock Unit Award Agreement (Time-Based) (Directors) This Restricted Stock Unit Award Agreement (Time-Based) (this “Agreement”), dated as of [] [], 20[], is entered into by and between Eos Energy Enterprises, Inc., a Delaware corporation (the “Company”), and the Participant whose name appears on the signature page to this Agreement (the “Participant”).

Form of Employee Time-Based Restricted Stock Unit Award Agreement under the Eos Energy Enterprises, Inc. Amended and Restated 2020 Incentive Plan

Page 1 EOS ENERGY ENTERPRISES, INC. Restricted Stock Unit Award Agreement (Time-Based) This Restricted Stock Unit Award Agreement (Time-Based) (this “Agreement”), dated as of [] [], 20[], is entered into by and between Eos Energy Enterprises, Inc., a Delaware corporation (the “Company”), and the Participant whose name appears on the signature page to this Agreement (the “Participant”). The Company

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39291 EOS ENERGY ENTERPRISES

Eos Energy Enterprises Reports Second Quarter 2024 Financial Results Successful commissioning of state-of-the-art (SotA) manufacturing line and up to $315.5 million strategic investment from Cerberus provide capacity and capital to significantly scal

eoseearningsreleaseq2202 Eos Energy Enterprises Reports Second Quarter 2024 Financial Results Successful commissioning of state-of-the-art (SotA) manufacturing line and up to $315.

Second Amended and Restated 2020 Incentive Plan

Exhibit 10.1 Eos Energy Enterprises, Inc. Second Amended and Restated 2020 Incentive Plan (Effective as of July 25, 2024) 1. Establishment of the Plan, Effective Date, and Duration: (a) Establishment of the Plan and Effective Date: Eos Energy Enterprises, Inc. (f/k/a B. Riley Principal Merger Corp. II), a Delaware corporation (the “Company”), hereby establishes this incentive compensation plan to

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 25, 2024 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 25, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

Form of Indemnification Agreement for Preferred Stock directors.

Exhibit 10.1 INDEMNITY AGREEMENT THIS INDEMNITY AGREEMENT (this “Agreement”) is made effective as of , 2024, by and between Eos Energy Enterprises, Inc., a Delaware corporation (the “Company”), and (“Indemnitee”). RECITALS The Company believes that, in order to attract and retain highly qualified persons to serve as directors or in other capacities, including as officers, it must provide those per

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☒ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 24, 2024 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 24, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

EOSE / Eos Energy Enterprises, Inc. / Cerberus Capital Management II, L.P. Activist Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D Under the Securities Exchange Act of 1934 (Amendment No. 1)* EOS ENERGY ENTERPRISES, INC. (Name of Issuer) Common Stock, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) Cerberus Capital Management II, L.P. 875 Third Avenue, 11th Floor New York, NY 10022 (212) 891-2100 Attn: Alex

Eos Energy Announces Compliance with Nasdaq Continued Listing Criteria EDISON, N.J., July 11, 2024 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) ("Eos" or the “Company”), a leading provider of safe, scalable, efficient, and sustainable zinc-based lon

eos-prnasdaqregaincompli Eos Energy Announces Compliance with Nasdaq Continued Listing Criteria EDISON, N.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 9, 2024 EOS ENERGY ENTERPRIS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 9, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

EOSE / Eos Energy Enterprises, Inc. / Cerberus Capital Management II, L.P. Activist Investment

SC 13D 1 formsc13d-eosenergy.htm UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D Under the Securities Exchange Act of 1934 (Amendment No. )* EOS ENERGY ENTERPRISES, INC. (Name of Issuer) Common Stock, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) Cerberus Capital Management II, L.P. 875 Third Avenue, 11th Floor New York, NY

Calculation of Filing Fee Table

EXHIBIT 107 Calculation of Filing Fee Table Form S-8 (Form Type) Eos Energy Enterprises, Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter)

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 3690 84-4290188 (State or other jurisdiction of incorporation) (Primary Standard Industrial Classification Code Number) (IRS Employer Identification No.) 3920 Park Avenue

Form of Insurer Letter Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and ACP Post Oak Credit I LLC

Exhibit 10.5 CONFIDENTIAL June 21, 2024 EOS Energy Enterprises, Inc. 3920 Park Ave, Edison, NJ 08820 Attention: [xxx] Phone: [xxx] Email: [xxx] Form of Insurer Letter Agreement Ladies and Gentlemen: Reference is made to the Senior Secured Term Loan Credit Agreement, dated as of July 29, 2022 (as amended, restated, supplemented or otherwise modified on or prior to the date hereof, the “Credit Agree

Form of Atlas Payoff Letter Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and ACP Post Oak Credit I LLC

Exhibit 10.4 Form of Payoff Letter June 21, 2024 EOS Energy Enterprises, Inc. 3920 Park Ave, Edison, NJ 08820 Attention: [xxx] Phone: [xxx] Email: [xxx] Ladies and Gentlemen: Reference is made to that certain Senior Secured Term Loan Credit Agreement, dated as of July 29, 2022 (as amended, modified, supplemented, or restated from time to time prior to the date hereof, the “Credit Agreement”), by a

Investor presentation, dated June 24, 2024.

Exhibit 99.3 Eos Energy Enterprises June 24, 2024 Cerberus Strategic Investment 2 Forward - Looking Statements This presentation includes “forward - looking statements” within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995 . Forward - looking statements include, but are not limited to, statements regarding our expected revenue, contribution marg

Form of Atlas Payoff Letter Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and ACP Post Oak Credit I LLC.

Exhibit 10.4 Form of Payoff Letter June 21, 2024 EOS Energy Enterprises, Inc. 3920 Park Ave, Edison, NJ 08820 Attention: [xxx] Phone: [xxx] Email: [xxx] Ladies and Gentlemen: Reference is made to that certain Senior Secured Term Loan Credit Agreement, dated as of July 29, 2022 (as amended, modified, supplemented, or restated from time to time prior to the date hereof, the “Credit Agreement”), by a

Form of Warrant

Exhibit 10.3 THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY STATE AND MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED, HYPOTHECATED, TRANSFERRED OR ASSIGNED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT, OR PURSUANT TO AN AVAILABLE EXEMPTION FROM, OR IN A TRA

2

Exhibit 99.1 Eos Energy Announces Strategic Investment of up to $315.5 Million from Cerberus to Propel Eos’ Expansion and Path to Profitability Significant strategic investment supports Company’s growth plans in an accelerating long duration battery storage market and enables Eos to restructure existing debt TURTLE CREEK, Pa and NEW YORK, June 24, 2024 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE)

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): June 21, 2024 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): June 21, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

Eos Energy Enterprises June 24, 2024 Cerberus Strategic Investment 2 Forward - Looking Statements This presentation includes “forward - looking statements” within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform

Exhibit 99.3 Eos Energy Enterprises June 24, 2024 Cerberus Strategic Investment 2 Forward - Looking Statements This presentation includes “forward - looking statements” within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995 . Forward - looking statements include, but are not limited to, statements regarding our expected revenue, contribution marg

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): June 21, 2024 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): June 21, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

Form of Series B Preferred Stock Certificate of Designation.

Exhibit 99.2 FORM OF CERTIFICATE OF DESIGNATION OF SERIES B-[●] NON-VOTING CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of the State

Securities Purchase Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and Cerberus Capital Management L.P.

Exhibit 10.2 SECURITIES PURCHASE AGREEMENT This SECURITIES PURCHASE AGREEMENT (this “Agreement”) is dated as of June 21, 2024, by and among EOS ENERGY ENTERPRISES, INC., a Delaware corporation (the “Company”), and CCM DENALI EQUITY HOLDINGS, LP (the “Purchaser”). RECITALS A. The Company and the Purchaser are executing and delivering this Agreement in reliance upon the exemption from securities reg

FORM OF CERTIFICATE OF DESIGNATION SERIES B-[●] NON-VOTING CONVERTIBLE PREFERRED STOCK EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware)

Exhibit 99.2 FORM OF CERTIFICATE OF DESIGNATION OF SERIES B-[●] NON-VOTING CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of the State

Credit Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and CCM Denali Debt.

Exhibit 10.1 Execution Version CERTAIN INFORMATION IN THIS EXHIBIT MARKED [***] HAS BEEN EXCLUDED FROM THIS EXHIBIT BECAUSE IT IS BOTH (A) NOT MATERIAL AND (B) WOULD BE COMPETITIVELY HARMFUL IF PUBLICLY DISCLOSED CREDIT AND GUARANTY AGREEMENT dated as of June 21, 2024 among EOS ENERGY ENTERPRISES, INC., as Borrower, THE GUARANTORS PARTY HERETO, VARIOUS LENDERS, and CCM DENALI DEBT HOLDINGS, LP, as

Series A-1 Preferred Stock Certificate of Designation

Exhibit 3.1 CERTIFICATE OF DESIGNATION OF SERIES A-1 NON-VOTING NON-CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of the State of Del

Series A-1 Preferred Stock Certificate of Designation.

Exhibit 3.1 CERTIFICATE OF DESIGNATION OF SERIES A-1 NON-VOTING NON-CONVERTIBLE PREFERRED STOCK OF EOS ENERGY ENTERPRISES, INC. (Pursuant to Section 151 of the General Corporation Law of the State of Delaware) The undersigned, Michael Silberman, the Secretary of Eos Energy Enterprises, Inc., a corporation organized and existing under and by virtue of the General Corporation Law of the State of Del

Form of Warrant.

Exhibit 10.3 THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY STATE AND MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED, HYPOTHECATED, TRANSFERRED OR ASSIGNED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT, OR PURSUANT TO AN AVAILABLE EXEMPTION FROM, OR IN A TRA

Securities Purchase Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and CCM Denali Equity.

Exhibit 10.2 SECURITIES PURCHASE AGREEMENT This SECURITIES PURCHASE AGREEMENT (this “Agreement”) is dated as of June 21, 2024, by and among EOS ENERGY ENTERPRISES, INC., a Delaware corporation (the “Company”), and CCM DENALI EQUITY HOLDINGS, LP (the “Purchaser”). RECITALS A. The Company and the Purchaser are executing and delivering this Agreement in reliance upon the exemption from securities reg

Credit Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and Cerberus Capital Management L.P.

Exhibit 10.1 Execution Version CERTAIN INFORMATION IN THIS EXHIBIT MARKED [***] HAS BEEN EXCLUDED FROM THIS EXHIBIT BECAUSE IT IS BOTH (A) NOT MATERIAL AND (B) WOULD BE COMPETITIVELY HARMFUL IF PUBLICLY DISCLOSED CREDIT AND GUARANTY AGREEMENT dated as of June 21, 2024 among EOS ENERGY ENTERPRISES, INC., as Borrower, THE GUARANTORS PARTY HERETO, VARIOUS LENDERS, and CCM DENALI DEBT HOLDINGS, LP, as

Form of Indemnification Agreement for Preferred Stock directors.

Exhibit 10.6 INDEMNITY AGREEMENT THIS INDEMNITY AGREEMENT (this “Agreement”) is made effective as of , 2024, by and between Eos Energy Enterprises, Inc., a Delaware corporation (the “Company”), and (“Indemnitee”). RECITALS The Company believes that, in order to attract and retain highly qualified persons to serve as directors or in other capacities, including as officers, it must provide those per

Form of Insurer Letter Agreement, dated June 21, 2024, by and between Eos Energy Enterprises, Inc. and ACP Post Oak Credit I LLC.

Exhibit 10.5 CONFIDENTIAL June 21, 2024 EOS Energy Enterprises, Inc. 3920 Park Ave, Edison, NJ 08820 Attention: [xxx] Phone: [xxx] Email: [xxx] Form of Insurer Letter Agreement Ladies and Gentlemen: Reference is made to the Senior Secured Term Loan Credit Agreement, dated as of July 29, 2022 (as amended, restated, supplemented or otherwise modified on or prior to the date hereof, the “Credit Agree

Press Release, dated June 24, 2024.

Exhibit 99.1 Eos Energy Announces Strategic Investment of up to $315.5 Million from Cerberus to Propel Eos’ Expansion and Path to Profitability Significant strategic investment supports Company’s growth plans in an accelerating long duration battery storage market and enables Eos to restructure existing debt TURTLE CREEK, Pa and NEW YORK, June 24, 2024 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE)

Form of Indemnification Agreement for Preferred Stock directors

Exhibit 10.6 INDEMNITY AGREEMENT THIS INDEMNITY AGREEMENT (this “Agreement”) is made effective as of , 2024, by and between Eos Energy Enterprises, Inc., a Delaware corporation (the “Company”), and (“Indemnitee”). RECITALS The Company believes that, in order to attract and retain highly qualified persons to serve as directors or in other capacities, including as officers, it must provide those per

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

Eos Energy Enterprises, Inc. Conflict Minerals Report - December 31, 202

Exhibit 1.01 EOS ENERGY ENTERPRISES, INC. CONFLICT MINERALS REPORT FOR THE YEAR ENDED DECEMBER 31, 2023 Introduction Eos Energy Enterprises, Inc. (“we”, “us”, “our”, the “Company” or “Eos”) is submitting this Conflict Minerals Report (the “Report”) for the calendar year ended December 31, 2023, as required by Rule 13p-1 under the Securities Exchange Act of 1934 (the “Rule”). All terms used but not

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD Specialized Disclosure Report EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Commission file number 001-39291

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD Specialized Disclosure Report EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Commission file number 001-39291 Delaware 84-4290188 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification No.) 3920 Park Avenue, Edison, New Jersey 08820 (Address o

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 20, 2024 EOS ENERGY ENTERPRIS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 20, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

Certificate of Amendment to the Third Amended and Restated Certificate of Incorporation of the Company, as amended

EOS ENERGY ENTERPRISES, INC. Second Certificate of Amendment to The Third Amended and Restated Certificate of Incorporation FIRST: The present name of the corporation is Eos Energy Enterprises, Inc., a Delaware corporation (the “Corporation”). The original certificate of incorporation of the Corporation was filed with the Secretary of State of the State of Delaware on June 3, 2019. An Amended and

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 14, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissi

Amendment to the Amended and Restated 2020 Incentive Plan

Third Amendment to the Eos Energy Enterprises, Inc. Amended and Restated 2020 Incentive Plan This Third Amendment (this “Amendment”) to the Eos Energy Enterprises, Inc. Amended and Restated 2020 Incentive Plan (as amended, restated, replaced, supplemented, or otherwise modified from time to time, the “Plan”) is approved and adopted to be effective as of May 1, 2024 (the “Effective Date”). Backgrou

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39291 EOS ENERGY ENTERPRISE

Eos Energy Enterprises Reports First Quarter 2024 Financial Results and Announces Successful Completion of Factory Acceptance Testing Company successfully completes Factory Acceptance Testing on state-of-the-art manufacturing line 1; remains on sched

Eos Energy Enterprises Reports First Quarter 2024 Financial Results and Announces Successful Completion of Factory Acceptance Testing Company successfully completes Factory Acceptance Testing on state-of-the-art manufacturing line 1; remains on schedule for Q2 commissioning EDISON, N.

Eos Energy Announces Approval of All Proposals at 2024 Annual Stockholder Meeting EDISON, N.J., May 03, 2024 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) ("Eos" or the “Company”), a leading provider of safe, scalable, efficient, and sustainable zinc

eospressrelease-annualme Eos Energy Announces Approval of All Proposals at 2024 Annual Stockholder Meeting EDISON, N.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 1, 2024 EOS ENERGY ENTERPRISE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 1, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commissio

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): April 23, 2024 EOS ENERGY ENTERPR

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): April 23, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commis

Eos Energy Enterprises Provides Business Update Continued progress against December 2023 Strategic Outlook, releases preliminary first quarter 2024 results, and announces first quarter financial results and conference call timing April 23, 2024 — EDI

Eos Energy Enterprises Provides Business Update Continued progress against December 2023 Strategic Outlook, releases preliminary first quarter 2024 results, and announces first quarter financial results and conference call timing April 23, 2024 — EDISON, N.

ARS

EOS ENERGY ENTERPRISES, INC 2023 ANNUAL REPORT 1 2023 Annual Shareholder Letter A Message from Joe Mastrangelo, Chief Executive Officer Dear Fellow Shareholders, We continue to be excited about long duration energy storage’s future as every global demand forecast reveals that the world needs more reliable, affordable, and sustainable energy.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☒ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☒ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Amendment No. 1)

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Amendment No. 1) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended: December 31, 2023 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 EOS ENERGY ENTERPRISES, INC. Delaware 001-39291 84-4290188 (State or other ju

Policy relating to recovery of compensation

Eos Energy Enterprises, Inc. CLAWBACK POLICY Introduction The Board of Directors (the "Board") of Eos Energy Enterprises, Inc. (the "Company") believes that it is in the best interests of the Company and its shareholders to create and maintain a culture that emphasizes integrity and accountability and that reinforces the Company's pay-for-performance compensation philosophy. This policy has theref

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 4, 2024 EOS ENERGY ENTERPRI

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 4, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commiss

Eos Energy Enterprises Reports Fourth Quarter & Full Year 2023 Financial Results and Provides 2024 Outlook Full-year gross margins improved by 41% year over year EDISON, N.J. – March 4, 2024 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) ("Eos" or the

Eos Energy Enterprises Reports Fourth Quarter & Full Year 2023 Financial Results and Provides 2024 Outlook Full-year gross margins improved by 41% year over year EDISON, N.

Separation Agreement, dated January 19, 2024, by and between the Company and Melissa Berube

TRANSITION AND RESIGNATION AGREEMENT AND GENERAL RELEASE This TRANSITION AND RESIGNATION AGREEMENT AND GENERAL RELEASE (this “Agreement”) is made as of this day of January 2024, by and between Melissa Berube, with an address at 852 Northeast Emerson St, Portland, OR 97211, USA (“Executive”), and Eos Energy Enterprises, Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended: December 31, 2023 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 EOS ENERGY ENTERPRISES, INC. Delaware 001-39291 84-4290188 (State or other jurisdiction of inco

Employment Agreement, dated January 17, 2024, by and between the Company and Michael Silberman

Employment Agreement This Employment Agreement (this “Agreement”) is dated as of January 17, 2024 (the “Effective Date”), and is made by and between Eos Energy Enterprises, Inc.

Eos Energy Enterprises Inc / Point72 Asset Management, L.P. - EOS ENERGY ENTERPRISES, INC. Passive Investment

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G/A Under the Securities Exchange Act of 1934 (Amendment No. 2)* Eos Energy Enterprises, Inc. (Name of Issuer) Common Stock, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) December 31, 2023 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule

Eos Energy Enterprises Inc / CVI Investments, Inc. - SC 13G/A Passive Investment

CUSIP No: 29415C101 SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G (Rule 13d-102) INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO § 240.13d-1(b), (c) AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO § 240.13d-2. (Amendment No. 1)* Eos Energy Enterprises, Inc. (Name of Issuer) Common Stock, $0.0001 par value per share (Title of Class of Securities) 29415C101 (CUSI

JOINT FILING AGREEMENT PURSUANT TO RULE 13d-1(k)

EXHIBIT 99.1 JOINT FILING AGREEMENT PURSUANT TO RULE 13d-1(k) The undersigned acknowledge and agree that the foregoing statement on Schedule 13G is filed on behalf of each of the undersigned and that all subsequent amendments to this statement on Schedule 13G shall be filed on behalf of each of the undersigned without the necessity of filing additional joint filing agreements. The undersigned ackn

Eos Energy Enterprises Achieves “Power On” Status of all Motion Systems on its First State-of-the-Art Manufacturing Line and Provides Preliminary Results

Exhibit 99.1 Eos Energy Enterprises Achieves “Power On” Status of all Motion Systems on its First State-of-the-Art Manufacturing Line and Provides Preliminary Results February 13, 2024 — EDISON, N.J. — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”), a leading provider of safe, scalable, efficient, and sustainable zinc-based energy storage systems, today announced that it achi

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 13, 2024 EOS ENERGY ENTE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 13, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Com

Eos Energy Enterprises Inc / YA II PN, Ltd. - SC 13G/A Passive Investment

Page 1 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 AMENDMENT NO. 2 to SCHEDULE 13G Under the Securities Exchange Act of 1934 Eos Energy Enterprises, Inc. (Name of Issuer) Common Shares, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) December 31, 2023 (Date of Event, which Requires Filing of this Statement) Check the appropriate box t

JOINT FILING AGREEMENT

EXHIBIT 99.1 JOINT FILING AGREEMENT The undersigned hereby agree that the statement on Schedule 13G with respect to the equity securities of Eos Energy Enterprises, Inc. is, and any amendment thereto signed by each of the undersigned shall be, filed on behalf of each of the undersigned pursuant to and in accordance with the provisions of Rule 13d-1(k) promulgated under the Securities Exchange Act

Eos Energy Enterprises Inc / Wood River Capital, LLC - SC 13G/A Passive Investment

SC 13G/A 1 d740470dsc13ga.htm SC 13G/A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 4)* Eos Energy Enterprises, Inc. (Name of Issuer) Common Stock, par value $0.0001 per share (Title of Class of Securities) 29415C101 (CUSIP Number) December 31, 2023 (Date of Event Which Requires Filing of this Statemen

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 1, 2024 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 1, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

Eos Energy Enterprises Join Forces with SABIC Specialties to Produce a Specialty Light- Weight, Conductive Composite Thermoplastic for Eos Z3TM Battery Multiyear supply agreement supports scaling Eos’s Z3 battery production and reducing battery modul

Eos Energy Enterprises Join Forces with SABIC Specialties to Produce a Specialty Light- Weight, Conductive Composite Thermoplastic for Eos Z3TM Battery Multiyear supply agreement supports scaling Eos’s Z3 battery production and reducing battery module cost as part of Project AMAZE TURTLE CREEK, Pa.

Pricing Agreement dated January 31, 2024, by and between HI-POWER, LLC and SHP US LLC

1 Classification: Confidential January 31, 2024 Attn: Garrett Dutkiewicz HI-POWER, LLC (“HI-POWER” or “Buyer”) 200 Braddock Ave Turtle Creek, PA Re: Pricing Agreement for SABIC LNP STAT-KON™ and NORYL™-Branded PPE Resins (the “Agreement”) Dear Garrett, This Agreement, together with the attachments, which are incorporated herein by reference, set forth the pricing terms that govern the sale of LNP STAT-KON and NORYL-branded PPE resins for the purpose molding of tanks, lids and terminal mounting brackets (the “Product(s)”) listed on Attachment A by SHPP US LLC or by a local Affiliate of SHPP Holding BV (“SABIC” or “SHPP”) to HI-POWER’s third party processors (“Authorized Purchasers”) listed on Attachment B.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 31, 2024 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 31, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 17, 2024 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 17, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm

Amended and Restated Manufacturing Purchase and Supply Agreement dated January 8, 2024, by and between HI-POWER, LLC and TETRA Technologies, Inc.

ex101tetraagreement Page 1 of 21 AMENDED AND RESTATED MANUFACTURING, PURCHASE AND SUPPLY AGREEMENT FOR TETRA PUREFLOW ZINC BROMIDE PRODUCTS AND EOS ELECTROLYTE PRODUCTS This Amended and Restated Manufacturing Purchase and Supply Agreement (this “Amended Agreement”) is made effective as of the last date shown on the signature page (the “Effective Date”) and is between TETRA Technologies, Inc.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 8, 2024 EOS ENERGY ENTERP

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 8, 2024 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Commi

Eos Energy Enterprises and TETRA Technologies, Inc. Extend Partnership, Expanding Electrolyte Production Capacity Companies executed an agreement establishing TETRA as the preferred strategic supplier of electrolyte products for Eos TURTLE CREEK, PA.

ex991tetrapressrelease Eos Energy Enterprises and TETRA Technologies, Inc. Extend Partnership, Expanding Electrolyte Production Capacity Companies executed an agreement establishing TETRA as the preferred strategic supplier of electrolyte products for Eos TURTLE CREEK, PA., Jan. 9, 2024 — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) ("Eos" or the “Company”), a leading provider of safe, scalable, ef

34,482,759 Shares of Common Stock Common Warrants to Purchase 34,482,759 Shares of Common Stock 34,482,759 Shares of Common Stock Underlying Common Warrants Eos Energy Enterprises, Inc.

Filed pursuant to Rule 424(b)(5) Registration No. 333-275863 PROSPECTUS SUPPLEMENT (To Prospectus dated December 11, 2023) 34,482,759 Shares of Common Stock Common Warrants to Purchase 34,482,759 Shares of Common Stock 34,482,759 Shares of Common Stock Underlying Common Warrants Eos Energy Enterprises, Inc. We are offering 34,482,759 shares of our common stock, par value $0.0001 per share, and acc

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): December 14, 2023 EOS ENERGY ENTE

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): December 14, 2023 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Com

Form of Common Stock Purchase Warrant

Exhibit 4.1 COMMON STOCK PURCHASE WARRANT EOS ENERGY ENTERPRISES, INC. Warrant Shares: [] Initial Issue Date: December 19, 2023 THIS COMMON STOCK PURCHASE WARRANT (the “Warrant”) certifies that, for value received, [] or its assigns (the “Holder”) is entitled, upon the terms and subject to the limitations on exercise and the conditions hereinafter set forth, at any time on or after the date hereof

Eos Energy Announces Launch of Proposed $40M Public Offering

Exhibit 99.1 Eos Energy Announces Launch of Proposed $40M Public Offering December 14, 2023 EDISON, N.J., Dec. 14, 2023 (GLOBE NEWSWIRE) — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”), a leading provider of safe, scalable, efficient, and sustainable zinc-based long duration energy storage systems, today announced a proposed underwritten public offering in which it intends t

Underwriting Agreement dated December 14, 2023 between the Company and Cowen and Company, LLC and Stifel, Nicolaus & Company, Incorporated as Representatives of the Several Underwriters*

Exhibit 1.1 EOS ENERGY ENTERPRISES, INC. 34,482,759 Shares of Common Stock (par value $0.0001 per share) Warrants to Purchase 34,482,759 Shares of Common Stock UNDERWRITING AGREEMENT December 14, 2023 Cowen and Company, LLC Stifel, Nicolaus & Company, Incorporated As Representatives of the several Underwriters c/o Cowen and Company, LLC 599 Lexington Avenue New York, New York 10022 c/o Stifel, Nic

Eos Energy Announces Pricing of $50 Million Public Offering

Exhibit 99.2 Eos Energy Announces Pricing of $50 Million Public Offering December 15, 2023 EDISON, N.J., Dec. 14, 2023 (GLOBE NEWSWIRE) — Eos Energy Enterprises, Inc. (NASDAQ: EOSE) (“Eos” or the “Company”), a leading provider of safe, scalable, efficient, and sustainable zinc-based long duration energy storage systems, today announced the pricing of an underwritten public offering of (i) 34,482,7

Subject to Completion, dated December 14, 2023

Filed pursuant to Rule 424(b)(5) Registration No. 333-275863 The information in this preliminary prospectus supplement is not complete and may be changed. A registration statement relating to these securities has been declared effective by the Securities and Exchange Commission. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities, and we

December 7, 2023

December 7, 2023 VIA EDGAR SUBMISSION Ms. Jenny O’Shanick Division of Corporation Finance U.S. Securities and Exchange Commission 100 F Street, N.E. Washington, DC 20549-3628 Re: Eos Energy Enterprises, Inc. Registration Statement on Form S-3 File No. 333-263298 Request for Withdrawal of Acceleration Request Dear Ms. O’Shanick: Eos Energy Enterprises, Inc. (the “Company”) respectfully withdraws it

LETTER

United States securities and exchange commission logo December 7, 2023 Nathan Kroeker Chief Financial Officer Eos Energy Enterprises, Inc.

December 7, 2023

December 7, 2023 VIA EDGAR SUBMISSION Ms. Jenny O’Shanick Division of Corporation Finance U.S. Securities and Exchange Commission 100 F Street, N.E. Washington, DC 20549-3628 Re: Eos Energy Enterprises, Inc. Registration Statement on Form S-3 File No. 333-263298 Request for Acceleration Dear Ms. O’Shanick: Pursuant to Rule 461 under the Securities Act of 1933, as amended, Eos Energy Enterprises, I

December 7, 2023

December 7, 2023 VIA EDGAR SUBMISSION Ms. Jenny O’Shanick Division of Corporation Finance U.S. Securities and Exchange Commission 100 F Street, N.E. Washington, DC 20549-3628 Re: Eos Energy Enterprises, Inc. Registration Statement on Form S-3 File No. 333-275863 Request for Acceleration Dear Ms. O’Shanick: Pursuant to Rule 461 under the Securities Act of 1933, as amended, Eos Energy Enterprises, I

As filed with the Securities and Exchange Commission on December 1, 2023

As filed with the Securities and Exchange Commission on December 1, 2023 Registration No.

Form T-1 Statement of Eligibility under the Trust Indenture Act of 1939 of the Trustee under the 5%/6% Convertible Senior PIK Toggle Notes Due 2026 Indenture

Exhibit 25.2 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM T-1 ☐ Check if an Application to Determine Eligibility of a Trustee Pursuant to Section 305(b)(2) WILMINGTON TRUST, NATIONAL ASSOCIATION (Exact name of trustee as specified in its charter) 16-1486454 (I.R.S. employer identification no.) 1100 North Market Street Wilmington, DE 19890-0001 (Address of principal

Form T-1 Statement of Eligibility under the Trust Indenture Act of 1939 of the Trustee under the Senior Notes Indenture

Exhibit 25.1 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM T-1 ☐ Check if an Application to Determine Eligibility of a Trustee Pursuant to Section 305(b)(2) WILMINGTON TRUST, NATIONAL ASSOCIATION (Exact name of trustee as specified in its charter) 16-1486454 (I.R.S. employer identification no.) 1100 North Market Street Wilmington, DE 19890-0001 (Address of principal

Filing Fee Table

Exhibit 107 Calculation of Filing Fee Table Form S-3 (Form Type) EOS ENERGY ENTERPRISES, INC.

Form of Senior Note (included in Exhibit 4.3 hereto)

Exhibit 4.3 EOS ENERGY ENTERPRISES, INC. as Issuer and Wilmington Trust, NATIONAL ASSOCIATION as Trustee SENIOR INDENTURE Dated as of [ ], 2023 SENIOR DEBT SECURITIES EOS ENERGY ENTERPRISES, INC. CERTAIN SECTIONS OF THIS INDENTURE RELATING TO SECTIONS 310 THROUGH 318, INCLUSIVE, OF THE TRUST INDENTURE ACT OF 1939: Trust Indenture Act Section Indenture Section 310(a)(1) and (2) 5.08 310(a)(3) and (

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39291 EOS ENERGY ENTERP

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 6, 2023 EOS ENERGY ENTER

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 6, 2023 EOS ENERGY ENTERPRISES, INC. (Exact name of registrant as specified in its charter) Delaware 001-39291 84-4290188 (State or other jurisdiction of incorporation) (Comm