This is the maximum amount of power it can dispatch. I think they use it intentionally so they can compare it to other generation sources.
For example this spreadsheet [1], with data for 2023, contains figures for "power capacity megawatts" and "energy capacity megawatthours".
1. https://www.eia.gov/analysis/studies/electricity/batterystor...
> In Q2 2026, battery energy stationary storage (BESS) installations reached 20.2 GWh
> total module manufacturing capacity to over 100 GWh.
> Storage Deployed in 2025: 57.6 GWh