At the end of 2021, the United States had 4,605 megawatts (MW) of operational utility-scale battery storage power capacity, according to our latest Preliminary Monthly Electric Generator Inventory. Power capacity refers to the greatest amount of energy a battery can discharge in a given moment. Batteries used for grid services have relatively short average durations. A battery’s average duration is the amount of time a battery can contribute electricity at its nameplate power capacity until it runs out. Batteries used for electricity load shifting have relatively long durations.