UPS Battery Runtime Calculator
Estimate how long a UPS or battery backup will run a load. Enter the battery energy in watt-hours, or its voltage and amp-hours, along with the load in watts and an efficiency, to see the runtime in minutes and hours.
How to estimate UPS runtime
- Enter the battery energy in watt-hours, or its voltage and amp-hours.
- Enter the load on the UPS in watts.
- Adjust the efficiency if needed, otherwise leave the default.
- Read the estimated runtime in minutes and hours.
Examples
1000 Wh battery powering a 300 W load
1000 Wh, 300 W load, 0.9 efficiency
About 180 minutes, or 3 hours
Frequently asked questions
How is UPS runtime estimated?
Usable energy is the battery watt-hours times the efficiency. Dividing by the load in watts gives hours, which the tool also shows in minutes.
How do I find my battery watt-hours?
Multiply the battery voltage by its amp-hours. A 12 volt 100 Ah battery is 1200 watt-hours. The tool can do this if you enter volts and amp-hours.
Why is real runtime often shorter?
Lead-acid batteries deliver less at high loads, called the Peukert effect, and you should not fully drain them. Treat this as an upper estimate.
What efficiency should I use?
Around 0.9 is typical for a UPS inverter. Older or heavily loaded units may be a little lower, which shortens the runtime.
Does a bigger load always cut runtime?
Yes. Runtime is inversely proportional to the load, so doubling the watts roughly halves the time the battery lasts.
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