UL 2743, UL 9540 and UL 1973 explained: what a power station's safety listing actually covers

Every product card on this site has a certification line, and on most of them it reads “none stated by the maker” in amber. That line is about three different standards, and the makers’ pages blur them constantly. UL 2743 is the listing for a portable power pack. UL 9540 is the listing for an installed energy storage system, with UL 1973 for the battery inside it. A UL94 flame rating is neither, and it is the one most often printed. Here is each in UL’s own scope language, and what a listing does and does not tell you.

UL 2743: portable power packs

UL’s standard 2743 covers, in its own words, portable and movable power packs provided with one or more batteries to power appliances or equipment on site, with lithium-ion capacity limited to an aggregate of 20 kWh, and with categories for indoor use, temporary outdoor use and outdoor use. That is a power station. A unit listed to it has had its battery, inverter, charging, enclosure and protections evaluated as a product, under the use category on its label. UL is explicit that phone power banks are a different standard, UL 2056, which is why a 74 Wh bank and a 2 kWh unit are not compared on this site.

This is the listing to look for on any unit you will plug a refrigerator into in a basement. Look for it on the unit itself and in the manual; a page that says “UL certified” without a number is not stating it.

UL 9540 and UL 1973: installed systems and their batteries

UL 1973 is the standard for batteries and battery modules used in stationary applications. UL 9540 is the standard for the energy storage system as a whole: the battery, the power conversion equipment, the controls and the way they work together. UL states the relationship directly: a UL 9540 system is primarily a UL 1973 battery evaluated together with a UL 1741 inverter as a system. UL 9540A, which also appears on datasheets, is a test method for how a system behaves in thermal runaway, used by fire codes, not a product listing on its own.

These are the listings that installed home batteries carry, and that building inspectors ask for. Tesla’s Powerwall 3 datasheet and FranklinWH’s aPower 2 datasheet both state UL 9540, and FranklinWH also states UL 9540A, UL 1973 and UL 1741; the whole-house page has the table. UL’s own Code Authority guidance notes that portable power packs are generally not evaluated as energy storage systems, which is why a 2 kWh unit on wheels should not be expected to carry UL 9540, and why it is notable when one does: EcoFlow states UL 9540 for the DELTA Pro 3 and both UL 9540 and UL 1973 for the DELTA Pro Ultra on the expandable roundup.

UL94: the one that is not a listing

UL94 is a flammability test for plastics. A rating of 94V-0 or 94-5VA describes how a sample of the enclosure material behaves in a flame test, and a fire-resistant casing is a good thing to have. It is not an evaluation of the battery, the inverter, the charger or the product, and it is not a product listing. EcoFlow’s DELTA 2 Max page cites a UL94-5VA casing; Jackery’s pages cite UL 94V-0. On this site those appear in the blurb as what they are, and the certification line stays at “none stated by the maker,” because it is.

What a listing tells you, and what it does not

A listing to UL 2743 or UL 9540 tells you an independent laboratory evaluated the product to a published standard and the maker submits to follow-up inspection. It does not tell you the unit’s usable capacity, its surge rating or its cycle life, and it does not make an inverter start a pump; those are the numbers the rest of this site is built on. It also does not tell you about chemistry: LiFePO4 cells are more tolerant of abuse than NMC, as the chemistry guide explains, but the chemistry is a property of the cell and the listing is a property of the product. Both matter; neither substitutes for the other.

How this site prints it

The certification line on every card prints exactly what the maker’s product page states, verbatim, on the date shown, and prints “none stated by the maker” otherwise. It does not upgrade a UL94 flame rating, a “UL certified” without a number, or a listing on a different model. When a maker adds the number to its page, the card changes on the next spec check. Until then, the label on the unit is the place to look.