By definition, a battery energy storage system (BESS) is an electrochemical apparatus that uses a battery to store and distribute electricity.

A BESS can charge its reserve capacity with power supplied from the utility grid or a separate energy source before discharging the electricity to its end consumer.

The number of large-scale battery energy storage systems installed in the US has grown exponentially in the early 2020s, with significant amounts of additional reserve capacity in development.