Battery Round-Trip Efficiency Calculator

Determine the round-trip efficiency of a battery system by comparing net discharge energy to the gross charge energy for the same cycle.

Gross energy supplied to the battery during the charge interval.
Energy exported from the battery terminals back to the load or grid.
Defaults to 0. Enter HVAC, pumping, or control losses tracked separately.

Engineering planning aid; validate against manufacturer test protocols or standards such as IEC 62619 before certification reporting.

Examples

  • Charge 520 kWh, discharge 452 kWh, auxiliary 18 kWh ⇒ 83.46% round-trip efficiency
  • Charge 310 kWh, discharge 278 kWh, auxiliary left blank ⇒ 89.68% round-trip efficiency

FAQ

How should I measure charge and discharge energy?

Use revenue-grade meters or inverter logs that capture AC-side energy for the exact charge and discharge window you are evaluating.

What counts as auxiliary losses?

Include HVAC, battery management, pumps, or any site loads you attribute to the battery while it is operating. If you meter them separately, enter the kWh so efficiency reflects delivered energy.

Why can efficiency exceed 100%?

When charge and discharge windows are misaligned or meters are uncalibrated, the export energy can appear higher than the intake. The calculator flags this so you can investigate instrumentation before reporting results.

Can I analyze multiple cycles?

Average the inputs over the period or sum charge and discharge energy for all cycles, then run the calculator once to obtain a fleet-level round-trip efficiency.

Additional Information

  • Round-trip efficiency is reported as a percentage with two-decimal precision.
  • Auxiliary losses default to 0 kWh when left blank so the result still computes.
  • Use consistent kWh measurements collected over the same cycle window for all inputs.

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