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.
Estimated result
Ideal—
Typical—
Conservative—
These are estimates, not guaranteed performance.
Formula and method
Typical hours = V × Ah × DoD × inverter efficiency ÷ (AC load + inverter standby).
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 inverter efficiency in %.
- Inverter standby (W)
- Enter inverter standby in W.
- Conservative retained fraction (%)
- Enter conservative retained fraction in %.
Worked example
The default 12 V, 100 Ah bank produces the same 8.23-hour typical estimate when losses and standby are included.
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 6, 2026