UL 9540A:2025 Raises the Stakes for US Battery Storage Safety

UL 9540A:2025 guidance is increasingly shaping how US battery storage projects demonstrate safety to regulators, insurers, and investors

15 Jan 2026

America’s battery storage boom is entering a more cautious phase. As ever larger lithium ion systems spread across the country, safety is no longer a background concern. It is becoming a central test of whether projects win permits, insurance and finance at all.

That shift is reflected in the growing influence of UL 9540A:2025, the latest edition of a fire test method used to assess thermal runaway and related risks. It is not a regulation. Yet in practice it has become a reference point for regulators and fire marshals, and is embedded in standards such as NFPA 855. Developers now treat it as part of the cost of doing business.

UL 9540A has long served as a common language between engineers and authorities. The 2025 update sharpens that role. It sets out a more consistent framework for testing, aimed at systems that are growing larger, denser and more complex. Local officials increasingly rely on its results when judging proposals, especially where projects sit close to homes or businesses.

The most important change is the closer link between tests and real world designs. Results from a broadly similar system are no longer assumed to apply. Small changes in packaging, spacing, ventilation or monitoring can alter how a battery behaves in a worst case event. The new edition reflects lessons drawn from years of laboratory work and from fires that escaped it.

This is already changing industry behaviour. For manufacturers and system integrators, being “UL 9540A ready” is becoming a selling point alongside price and performance. Those able to provide configuration specific data early can smooth talks with planners and insurers. For developers, clearer evidence may reduce late stage redesigns, though much still depends on local interpretation.

UL Solutions says the fifth edition was shaped with input from industry and regulators, a sign of where expectations are heading. Wesley Kwok, its vice president for energy and industrial automation, has argued that the goal is to make products safer while allowing the storage market to grow.

The effects reach beyond engineers. Insurers, lenders and investors scrutinise safety evidence when judging operational risk. Better documentation can help reassure them, and the public, as batteries move closer to critical infrastructure.

Extra testing adds cost and weighs heaviest on smaller suppliers. Even so, many see it as unavoidable. For an industry that underpins electrification and renewable power, UL 9540A:2025 sends a clear message: safety proof is now part of the project, not an afterthought.