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Round-trip efficiency

Round-trip efficiency is the share of electricity put into storage that comes back out. A battery that takes in 100 MWh and returns 85 MWh is 85% efficient.

Also called RTE, round trip efficiency

Formula

Round-trip efficiency = energy out (MWh) ÷ energy in (MWh)

Full cycle
Starts and ends at the same state of charge
Same meter
Charging and discharge measured at the same point

With real numbersMenifee Power Bank, 2025: 845,778 MWh out ÷ 963,230 MWh in = 87.8%

In the data

86.1%of the energy US batteries took in during 2025 came back out

The fleet ratio rose from 78% in 2018 to 86% in 2025. It is a yearly flow ratio, close to but not the same as round-trip efficiency.

Discharged over charged energy, US batteries, %
78%'18'19'20'21'22'23'2486%'25

EIA-923 battery charging and discharge, complete reporting years, projects that report both.On the map

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

Common mistakes

  1. Using a month's discharge over charging as the efficiency. If the battery ended fuller or emptier than it started, the ratio is off.
  2. Ignoring auxiliary load. Cooling and controls draw power that may sit on a different meter.
  3. Comparing cell figures with grid figures. Efficiency measured at the cells is higher than what the grid meter sees.

How the InfraMap analyst defines it

Electrical energy recovered relative to charging energy for a compatible cycle and meter boundary. A period discharge/charge ratio is not RTE when start/end stored energy or metering boundaries differ.

RTE = discharged MWh / charged MWh only for an energy-balanced compatible cycle

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

Primary references

See it for any US plant

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