UPS Battery Runtime Calculator
Find out how long your UPS backup will last in a power cut. Enter your battery details, the load you run on it, and inverter efficiency to get the estimated backup time.
Battery and load details
Usable capacity: use 50 for lead-acid batteries, 80 to 90 for lithium batteries. Efficiency is usually 80 to 90 for home inverters.
Estimated backup time
—
| Total stored energy | — |
|---|---|
| Usable energy (after depth of discharge) | — |
| Energy reaching your load (after efficiency) | — |
| Runtime in minutes | — |
| Runtime in hours (decimal) | — |
This is a planning estimate. Battery age, temperature and wiring losses change the real runtime.
How to use
- Enter how many batteries you have, the Ah rating written on each battery, and the voltage (usually 12 V).
- Add the total watts of everything you run on the UPS, for example fans, lights and a TV.
- Set inverter efficiency and usable capacity, then press Calculate Runtime.
- Read the backup time and the energy breakdown in the results card.
Note: To measure your real load, add up the wattage printed on each device label. A typical ceiling fan uses 70 to 80 watts and an LED bulb uses 9 to 12 watts.
Tips
- Lead-acid batteries live longest when you keep usable capacity at 50 percent.
- Running a smaller load doubles the runtime, so switch off heavy devices during long cuts.
- Old batteries lose capacity over time, so reduce the usable capacity setting for batteries older than 2 years.
- High temperature shortens backup time, so keep the UPS and batteries in a cool, ventilated place.