Battery energy storage (BESS)

A battery energy storage system charges from the grid or a solar farm and discharges later. Its MW rating says how fast it can discharge, its MWh rating says how much, and together they give its duration.

Also called BESS, battery storage, storage duration

Formula

Duration (hours) = usable energy (MWh) ÷ discharge power (MW)

Usable energy: The MWh the battery can deliver, not the larger cell total
Discharge power: The MW it can deliver at once

With real numbersMenifee Power Bank: 2,720 MWh ÷ 680 MW = 4.0 hours

In the data

47%of US battery power can discharge for about four hours

Four hours is the most common design: 25.2 GW of 53.9 GW. Most of the rest discharge for one or two hours.

US battery power by duration, GW

EIA-860M battery power and energy capacity for 1,053 US projects.On the map

Built from InfraMap's 2025 data with the same tools the analyst uses.

Common mistakes

Dividing ratings from different dates or meter points. Batteries get expanded over time, and AC and DC ratings differ.
Reading net generation as battery use. A battery's net MWh is discharge minus charging, so it hides both.
Judging a battery by how often it cycles. One that rarely discharges can still be paid to hold reserves.

How the InfraMap analyst defines it

Battery energy storage system and energy storage resource. MW discharge rating and usable MWh must share vintage and AC/DC boundary for duration.

Nominal duration hours = compatible usable MWh / discharge MW

Reviewed October 1, 2026 against the references below. The analyst and the MCP server answer with this definition.

Primary references

Grid-scale battery storage FAQnlr.gov
Battery efficiency and utilization assumptionsatb.nlr.gov

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