Battery system failures fell 98% in 7 years, but older systems need special care: report

Dive Brief:

• The global failure rate for lithium-ion battery energy storage systems, on a per-GWh basis, fell 98% from 2018 to 2025 and 50% from 2024 to 2025, the Electric Power Research Institute said in a new analysis of its BESS failure incident database.
• Stationary energy storage systems’ annual failure rates range from 0.04% to 0.14%, according to the analysis. That is comparable to the 0.1% annual failure rate for oil-filled electrical transformers, EPRI said in the report, Risk Factors and Failure Statistics of Lithium-Ion BESS.
• Safety reviews and, in some cases, retrofits can mitigate failure risk and improve reliability in older systems, which tend to fail at higher rates than newer systems built under stricter codes and design practices, EPRI said.

Dive Insight:

Ninety-three percent of the BESS safety incidents EPRI reviewed worldwide resulted in no injuries or fatalities, according to the report. 

In the United States, no reported injuries or fatalities have occurred as a result of BESS failures since April 2019, when an explosion at an Arizona Public Service facility seriously injured four firefighters. A post-incident report by Underwriters Laboratories, the global safety science organization known as UL, noted that the APS installation was commissioned before the initial release of NFPA 855, the safety standard that governs energy storage systems today. 

As soon as this fall, the National Fire Protection Association plans to replace NFPA 855 with NFPA 800, which it calls a “holistic” standard that incorporates lessons learned since the early days of BESS deployment.

Lakshmi Srinivasan, a senior technical leader with EPRI’s energy storage program and a principal investigator on the report, told Utility Dive that battery systems deployed over the past five years appear significantly more reliable than earlier vintages. The trend continues today.

“There are things we know in 2026 that were not necessarily understood in 2019 or 2020, when the older systems were being put in place,” Srinivasan said in an interview.

The most dramatic BESS failure in the U.S. involved a utility-scale installation inside a 1950s-era turbine hall at a decommissioned thermal power plant near Santa Cruz, California, known as Moss Landing. In January 2025, thermal runaway in one of the units caused fire to spread throughout the indoor facility and ultimately destroyed most of the 300-MW battery array. Thick smoke emanated from the facility for days, but no injuries were reported and subsequent soil and water monitoring found no significant threats to human health or the environment.

Experts later told Utility Dive the incident was a “learning opportunity” for the energy storage industry. 

Indoor BESS facilities fail at higher rates and sustain more damage on average than outdoor facilities, according to EPRI’s report. Propagation-prevention measures within battery units and fire walls or similar barriers between units can mitigate fire’s spread within indoor facilities, EPRI said.

Vistra commissioned Moss Landing in 2020. BESS facilities commissioned before 2021 account for just 3% of global energy storage capacity, according to the report. It’s worthwhile for owners of those older facilities to run thorough risk assessments of them and take corrective action if warranted, Srinivasan said.

For example, the 2019 incident in Arizona showed a need for older BESS facilities to address explosion risk, which represents “a different risk than fire and a bigger one from a personnel and equipment standpoint,” Srinavasan said. 

Explosion-mitigation retrofits range from what she called “a relatively low-difficulty change,” like installing flammable gas detectors inside battery enclosures, to more significant projects like installing new ventilation systems or making structural upgrades to direct pressure waves upward and away from first responders, Srinavasan said. 

Those last two types of projects generally require changes to battery unit envelopes, which could void the manufacturer’s warranty or interfere with other aspects of the system’s design, Srinavasan said. In some scenarios, it could make more sense to prematurely decommission an outdated, higher-risk system, she added.

Although newer battery systems appear to be safer than early-vintage systems, local permitting remains challenging in some jurisdictions due to limitations in the NFPA 855 standard that lead most developers to apply for exemptions to allow for higher energy densities or other project modifications, Srinavasan said. 

To assist local authorities that may lack in-house expertise, New York added a requirement to its fire code — which took effect in January — that those authorities can make energy storage developers pay for independent technical reviews of exemption applications, she added.