Independent Fire Testing Confirms Eos Z3 Battery System Exhibited No Thermal Runaway, No Sustained Fire, and No Propagation Under Abuse Testing; Company Receives ISO 14001 Certification

Energy Safety Response Group testing found no thermal runaway, no sustained fire, and no propagation under direct flame impingement and overcharge abuse, supporting safe siting of long-duration storage in dense urban environments

Third-party testing addresses evolving NFPA 855 fire-test expectations and reinforces Eos’ differentiated safety profile

PITTSBURGH, June 22, 2026 (GLOBE NEWSWIRE) -- Eos Energy Enterprises, Inc. (NASDAQ:EOSE) ("Eos" or the "Company"), America's leading innovator in designing, manufacturing and providing zinc-based long-duration energy storage systems sourced and manufactured in the United States, today announced the results of independent destructive testing of its Eos Z3™ battery modules. Energy Safety Response Group (ESRG), an independent energy storage safety and fire testing organization, conducted testing equivalent to large-scale fire testing (LSFT). Under the conditions tested, the modules exhibited no thermal runaway, no sustained fire, and no propagation to adjacent live modules.

The 2026 edition of NFPA 855, the standard governing the installation of stationary energy storage systems, now requires large-scale fire testing to confirm that a system failure does not spread between units at specified spacing. To address these evolving requirements, Eos subjected modules to two severe abuse scenarios: direct flame impingement and overcharge. Even with active flame applied, the modules did not enter thermal runaway, did not sustain fire, and did not propagate to adjacent modules. The tests also showed no ignition of off-gas.

"The inherent fire safety of our zinc aqueous chemistry has been foundational to Eos from the beginning," said Francis Richey, Eos Chief Technology Officer. "Independent testing using LSFT-equivalent methods turns that design into validated performance. Under direct flame and overcharge, the Z3 modules did not experience thermal runaway, sustain fire, or propagate failure. These are the outcomes that matter most to customers, regulators, first responders, and the communities that host our systems."

The results reflect the inherent safety advantages of Eos’ water-based electrolyte and flame-retardant polymer architecture, which give long-duration storage a fundamentally different fire and thermal runaway risk profile than conventional chemistries. ESRG evaluated the modules under conditions more severe than those typically expected in real-world applications.

High-voltage, large-scale energy storage systems carry inherent electrical risks similar to those found in any type of power plant. Testing equivalent to large-scale fire testing is essential to understanding how these systems behave under failure conditions. In such destructive testing, the Eos battery module demonstrated a distinct safety profile, with no evidence of thermal runaway or propagation, outcomes that are highly relevant for effective risk mitigation, informed project siting, and ensuring long-term asset reliability.

"As energy storage becomes a larger part of our nation's energy infrastructure, communities need confidence that safety is being prioritized," said Matthew Brown, Chief of the Allegheny County Department of Emergency Services. "In November 2025, my department, along with several municipal departments, responded to an incident involving overcharged battery modules at Eos' Turtle Creek facility. Even under that real-world stress, the system did not enter thermal runaway or escalate into a fire event. Eos' recent independent fire test further validates what we witnessed firsthand in the field."

"Energy storage is now critical infrastructure, and critical infrastructure has to be safe enough to sit close to where people live and work," said Joe Mastrangelo, Eos Chief Executive Officer. "As data centers, utilities, and industrial users add storage inside dense urban environments, the market needs systems that scale without adding fire risk. ESRG’s independent testing validates that Eos technology is built to do exactly that, and it speaks directly to the siting, permitting, and insurance questions that shape where storage can go."

Separately, Eos announced it has achieved ISO 14001 certification, the globally recognized standard for environmental management systems (EMS), following a comprehensive third-party evaluation. This certification confirms that Eos maintains robust environmental management practices that strengthen operational performance, risk management, and cost efficiency. The achievement reflects the maturity of Eos’ environmental practices across its operations and manufacturing facilities.

ESRG’s independent test results and the ISO 14001 certification provide third-party validation of Eos’ core technology and manufacturing operations, reinforcing the differentiated safety profile of Eos’ zinc-based chemistry as Eos scales toward 4 GWh of annual production capacity across its Turtle Creek and recently commercialized Thorn Hill facilities.

About Eos Energy Enterprises

Eos is accelerating the shift to American energy independence with positively ingenious solutions that transform how the world stores power. The Company’s BESS features the innovative Znyth™ technology, a proven chemistry with readily available non-precious earth components, designed to provide a safe, secure, stable, and scalable alternative to conventional technologies. The Company’s BESS is ideal for utility-scale, microgrid, commercial, and industrial long-duration energy storage applications (i.e., 4 to 16+ hours) and provides customers with significant operational flexibility to cost effectively address current and future increased grid demand and complexity. For more information about Eos (NASDAQ:EOSE), visit www.eose.com.

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Forward Looking Statements

Except for the historical information contained herein, the matters set forth in this press release are 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 that refer to outlook, projections, forecasts or other characterizations of future events or circumstances, including any underlying assumptions, including statements regarding the expected implications of the ESRG testing results, the anticipated benefits of the Company’s technology and environmental management systems, the Company’s targeted production capacity, and future customer adoption, project deployments, and commercial opportunities. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intends," "may," "might," "plan," "possible," "potential," "predict," "project," "should," "would" and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. Forward-looking statements are based on our management’s beliefs, as well as assumptions made by, and the information currently available to, them. Because such statements are based on expectations as to future financial and operating results and are not statements of fact, actual results may differ materially from those projected.

Factors which may cause actual results to differ materially from current expectations include, but are not limited to: changes adversely affecting the business in which we are engaged; our ability to forecast trends accurately; our ability to generate cash, service indebtedness and incur additional indebtedness; our ability to raise financing in the future; risks associated with the credit agreement with Cerberus, including risks of default, dilution of outstanding Common Stock, contractual lockup of shares; our customers’ ability to secure project financing; the timing, issuance and size of future project-level purchase orders and the conversion of framework agreements, backlog and pipeline into revenue; the ability of counterparties to perform under the Master Supply Agreement; risks associated with entering and operating in international markets, including regulatory, permitting, tax and supply chain considerations; the amount of final tax credits available to our customers or to Eos pursuant to the Inflation Reduction Act; the timing and availability of future funding under the Department of Energy Loan Facility; our ability to continue to develop efficient manufacturing processes to scale and to forecast related costs and efficiencies accurately; fluctuations in our revenue and operating results; competition from existing or new competitors; risks related to project development, construction and commissioning timelines; our ability to convert firm order backlog and pipeline to revenue; risks associated with security breaches in our information technology systems; risks related to legal proceedings or claims; risks associated with evolving energy policies in the United States and other countries and the potential costs of regulatory compliance; risks associated with changes to the U.S. trade environment; our ability to maintain the listing of our shares of common stock on NASDAQ; our ability to grow our business and manage growth profitably, maintain relationships with customers and suppliers and retain our management and key employees; risks related to the adverse changes in general economic conditions, including inflationary pressures and increased interest rates; risk from supply chain disruptions and other impacts of geopolitical conflict; changes in applicable laws or regulations; the possibility that Eos may be adversely affected by other economic, business, and/or competitive factors; other factors beyond our control; risks related to adverse changes in general economic conditions; and other risks and uncertainties.

The forward-looking statements contained in this press release are also subject to additional risks, uncertainties, and factors, including those more fully described in the Company’s most recent filings with the Securities and Exchange Commission, including the Company’s most recent Annual Report on Form 10-K and subsequent reports on Forms 10-Q and 8-K. Further information on potential risks that could affect actual results will be included in the subsequent periodic and current reports and other filings that the Company makes with the Securities and Exchange Commission from time to time. Moreover, the Company operates in a very competitive and rapidly changing environment, and new risks and uncertainties may emerge that could have an impact on the forward-looking statements contained in this press release.

Forward-looking statements speak only as of the date they are made. Readers are cautioned not to put undue reliance on forward-looking statements, and, except as required by law, the Company assumes no obligation and does not intend to update or revise these forward-looking statements, whether as a result of new information, future events, or otherwise.