UL 1973
Safety of the battery pack itself — cells against thermal runaway and mechanical stress.
What UL 1973 covers
The battery pack as a component: cell chemistry safety, thermal runaway containment, and mechanical abuse. It certifies the pack, not the whole storage system around it.
Why it matters for balcony solar
Storage is optional and the most expensive piece of a balcony setup, but it's what lets you use midday solar after dark. UL 1973 is the pack-level standard, and it's the battery standard UL 3700's reference chain includes.
The common mix-up
UL 1973 covers the pack only. The complete storage system — battery plus its inverter plus the software coordinating them — is a different, higher-level standard (UL 9540), and that one is NOT in UL 3700's chain.
UL 1973 is one of several UL standards behind a plug-in system. See how they fit together →
What to look for when buying
UL 1973 covers the pack. For a whole battery system, also look for UL 9540.