How to Calculate Battery Runtime
Calculate realistic battery runtime from usable watt-hours, average load, efficiency and reserve.
Calculate realistic battery runtime from usable watt-hours, average load, efficiency and reserve.
Enter your own equipment values. The calculator uses transparent assumptions so you can adjust efficiency, reserve and operating conditions.
Use Real Equipment Ratings
Calculate realistic battery runtime from usable watt-hours, average load, efficiency and reserve.
Calculator Guidance
Use the result for planning, then verify the exact product manual, nameplate ratings and operating limits.
Battery Runtime Calculator
Planning estimate only.
Formula
Runtime hours = battery Wh × efficiency × (1 − reserve) ÷ load watts.
Examples
| Battery | Load | Efficiency/Reserve | Estimated Runtime |
|---|---|---|---|
| 512Wh | 60W | 85% / 10% | About 6.5 hours |
| 1024Wh | 150W | 85% / 10% | About 5.2 hours |
| 2048Wh | 500W | 90% / 10% | About 3.3 hours |
What Changes Runtime
Battery Age
Older batteries deliver less energy.
Temperature
Cold reduces available capacity.
Inverter Losses
AC loads use more than nameplate energy.
Duty Cycle
Refrigerators and pumps cycle.
Surge Loads
Startup can trip output limits.
Reserve Settings
Systems stop before complete depletion.
Frequently Asked Questions
What is the basic runtime formula?
Usable watt-hours divided by average watts.
Why is actual runtime lower?
Conversion losses, reserve, temperature and battery age.
Should I use surge watts?
Use average running watts for runtime and surge watts for compatibility.
How do cycling appliances change the result?
Use average duty-cycle wattage.
Can I use amp-hours?
Convert amp-hours to watt-hours using nominal voltage.
Is 100% discharge safe?
Use the manufacturer’s allowed depth of discharge.