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

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, 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.

Eos Energy Enterprises | www.eose.com