Free energy calculator

Inverter Battery Runtime Calculator

Estimate AC runtime from a battery bank while including inverter conversion loss and idle consumption.

Calculate your estimate

Change the example values to match your system.

V

Enter battery voltage in V. Supported input range: 0.01 to 10,000 V.

Ah

Enter nominal capacity in Ah. Supported input range: 1 to 1,000,000 Ah.

W

Enter ac load in W. Supported input range: 0.01 to 100,000 W.

%

Enter depth of discharge in %. Supported input range: 1 to 100 %.

%

Enter AC output power divided by DC input power for the load in use. Supported input range: 1 to 100 %.

W

Optional. Enter DC no-load draw separately, or 0 if it is already included in a measured total DC input. Supported input range: 0 to 100,000 W.

%

Enter conservative retained fraction in %. Supported input range: 1 to 100 %.

Estimated result

Ideal—

Typical—

Conservative—

Enter valid inputs and calculate to see results.

These are estimates, not guaranteed performance.

Formula and method

DC input watts = AC load ÷ inverter efficiency + DC-side standby. Typical hours = V × Ah × DoD ÷ DC input watts.

Percent fields are entered as percentages; the calculation converts them to decimal fractions.

Displayed results are rounded to two decimal places.

What the inputs mean

Battery voltage (V)
Enter battery voltage in V.
Nominal capacity (Ah)
Enter nominal capacity in Ah.
AC load (W)
Enter ac load in W.
Depth of discharge (%)
Enter depth of discharge in %.
Inverter efficiency (%)
Enter AC output power divided by DC input power for the load in use.
DC-side inverter standby (W)
Enter DC no-load draw separately, or 0 if it is already included in a measured total DC input.
Conservative retained fraction (%)
Enter conservative retained fraction in %.

Worked example

The default 12 V, 100 Ah bank provides about 8.27 typical hours after conversion loss and DC-side standby draw.

Why the real result may differ

  • Temperature, battery age, wiring resistance, and changing loads can move actual results away from the estimate.
  • Manufacturer ratings may be measured under different test conditions. Measure the load when practical.

Common mistakes

  • Do not confuse watts (power) with watt-hours (energy).
  • Do not enter a percentage as a whole number: 90% is entered as 90 in this form and converted internally.

Frequently asked questions

Is this result guaranteed?

No. It is an engineering estimate; equipment, temperature, age, and duty cycle affect real performance.

Why are three estimates shown?

The ideal case ignores practical losses, while typical and conservative cases apply the efficiency and margin entered above.

Related tools

References

Last reviewed: August 12, 2026