Battery Round-Trip Efficiency Calculator

Round-trip efficiency: calculation method

This page evaluates efficiency = output energy ÷ input energy × 100. Its variables correspond to Discharged energy and Charging energy.

Using the loaded examples gives 82.00%. Your saved case should identify where each entry came from.

Calculate round-trip efficiency from discharged energy and charging energy. The charging time step is handled by Battery Charging Time Calculator.

Preparing the calculation

Record chemistry, temperature, state of charge, age, and discharge rate. Write down whether each entry is measured, rated, assumed, or calculated.

Values used below a division bar must stay positive. A prefix error can move the result by several orders of magnitude.

Discharged energy

Default example: 820 Wh. Enter discharged energy in Wh.

Charging energy

Default example: 1000 Wh. Enter charging energy in Wh.

Applying the result

The primary answer, Round-trip efficiency, describes only the entered scenario. Compare it with manufacturer discharge data at the intended rate.

Save the raw entries before testing another scenario.

Checks before using the answer

Compare complete cycles with the same start and end state of charge.

A complete model can also include temperature, cell imbalance, BMS cutoffs, aging, and rate dependence. Do not hide omitted behavior inside an unexplained correction factor.

Record chemistry, temperature, state of charge, age, and discharge rate.

Sensitivity check

Change Discharged energy from 820 Wh to 984 Wh and preserve the rest of the case. This moves the answer from 82.00% to 98.40%.

Use a separate scenario when multiple conditions change together.

Keep a reproducible record

Save discharged energy and charging energy with round-trip efficiency. Add the date and any unit conversion.

Carry round-trip efficiency as the raw numerical value until the final step. Do not round between dependent calculations.

Using this result in a larger analysis

Review discharged energy and the remaining entries as one case. If one value belongs to another temperature, load, or time period, separate the scenarios.

Use round-trip efficiency alongside a warm, cold, new, and aged battery case where relevant. Preserve the unrounded number until all dependent calculations and comparisons are complete.

Document any effect handled outside this page, especially voltage sag, thermal rise, charge taper, and balancing. That note prevents a later reader from assuming the simple equation covered it.

Questions from practical use