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Battery Round Trip Efficiency Calculator

Work out battery round trip efficiency instantly with clear inputs, formula shown and shareable results.

About Battery Round Trip Efficiency Calculator

Round-trip efficiency is energy out divided by energy in over a full charge and discharge cycle, measured at the same point in the system. Lithium systems achieve 85-95% at the DC terminals but 82-90% at the AC connection once inverter and auxiliary losses are included, and auxiliaries such as cooling matter at high ambient temperature.

Formulas

Round-trip efficiency

RTE % = energy discharged x 100 / energy charged

Annual loss

Annual loss = loss per cycle x cycles per year

Worked example

With the default values below, Battery Round Trip Efficiency Calculator returns Round-Trip Efficiency of 88.000%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Energy Chargedminimum 0 kWh
1,000 kWh
Energy Dischargedminimum 0 kWh
880 kWh
Cycles Per Yearminimum 0
350
Electricity Priceminimum 0 per kWh
4 per kWh

Results

Round-Trip Efficiency
88.000%
Energy Lost Per Cycle
120.000
Annual Energy Loss
42,000.0
Annual Cost Of Losses
$168,000.00

Step by step

  1. 1Values used
  2. 2Round-trip efficiency
  3. 3Annual loss
  4. 4Round-Trip Efficiency= 88.000
  5. 5Energy Lost Per Cycle= 120.000
  6. 6Annual Energy Loss= 42,000.0
  7. 7Annual Cost Of Losses= 168,000.00

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation or tax into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Should efficiency be measured at AC or DC?

At the point of connection that matters commercially, normally AC. DC-side figures exclude inverter and transformer losses and auxiliary consumption, so they flatter the system by 3-8 points.

Does efficiency change with C-rate?

Yes. Higher charge and discharge rates raise ohmic losses, so round-trip efficiency falls by several points at 1C compared with 0.25C.

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