UL9540 Second Edition: Fortress Batteries, Sol-Ark Inverter Meet New Requirements


Battery/Inverter Pairing Meets UL9540 Second Edition Requirements in the Most Stringent Jurisdictions

LANGHORNE, PA. (December 8, 2022) – Fortress Power is proud to announce that its eFlex and eVault Max batteries have passed a combined test to meet the standards of the Second Edition of UL9540.

Fortress Power received their confirmation of acceptance late last month. 

As UL9540 codes continue to evolve, Fortress Power takes pride in keeping its products up to the standards of the most stringent jurisdictions.  

The fundamental definition of UL9540 changed considerably from the first edition to the more recent UL9540 second edition.  

Initially, building applicable safety features into the battery met the specifications of UL9540 independent of all other components of the system.

But UL9540 Second Edition redefined the energy storage system entirely by requiring not only the battery’s safety features, but those of the inverter as well. 

This was a departure from protocol in that test standards have always been about specific products rather than entire systems. With UL9540’s Second Edition, inspectors are interpreting a need for every combination of battery and inverter to pass the test as a unit. 

UL9540 Second Edition


“To meet the requirements of UL9540 Second Edition as some jurisdictions interpret it, you have to test both the battery and the inverter together and in every possible permitted configuration,” explained John Cromer, Director of Product for Fortress Power.

“Nationally recognized test labs do not issue compatibility statements on products they have not tested.”

It’s important to note that nothing has changed in regard to the batteries themselves. Fortress Power batteries continue to contain all required safety features to meet the UL9540 standard, regardless of its partnering inverter.

Fortress batteries have met the UL9540 standards since the UL9540 first edition was published.

The aforementioned stringent jurisdictions are implementing the updated standards immediately, bypassing any previously accepted notion of a three-year ‘grace period’ common to other new standards within the building industry. 

Fortress Power Batteries, Partnering Inverters Meet Most Stringent Standards

Fortress Power continues to work to ensure that installers in these regions pass inspections with all applicable combinations of batteries and inverters. 

Fortress Power’s emphasis remains providing installers with the premier industry option while ensuring their ability to pass inspection even in areas with the strictest requirements.  

To that end, Fortress worked closely with Sol-Ark to meet the UL9540 Second Edition compliance for the eFlex and the eVault Max to be compatible with the Sol-Ark 15K inverters. 

Fortress Provides an All-in-One Solution for Installers

The news is music to the ears of installers in regions where inspectors are strictly interpreting the UL9540 Second Edition. These installers now have a solution with Fortress Power batteries.

“Fortress Power batteries have always had the relevant safety features built directly into the battery, regardless of the inverter that is used,” said Cromer. 

“The listing requirements and the associated building codes continue to evolve, but Fortress Power continues to maintain and increase its product certifications. This allows continued installation of our batteries in even the most stringent jurisdictions without issue.” 

Fortress endeavors to continue working with other manufacturers to continue expansion of product offerings.

To learn more about Fortress Power batteries, please contact your sales rep or email us at [email protected] 

About Fortress Power 

Headquartered in Langhorne, PA, Fortress Power is a leading global designer and manufacturer of Lithium Iron (LFP) battery energy storage systems for residential, commercial, and industrial customers.

The Company has operations across North America, the Caribbean, Central American and Asia. In addition to its award-winning local live technical support, Fortress Power has partnered with industry-leading lending institutions to help make investment in solar and storage as easy as possible. 


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