Battery run-time calculator
Choose one of our batteries or enter your own, add the device you want to run, and see how long one full charge will last. If you only know amp-hours and volts, or volts and amps, the calculator converts them for you.
The figures are estimates. They assume 85% of the battery’s rated energy is usable, and real run time depends on temperature, battery age and how the device is used.
Battery run-time calculator
Allows for inverter and conversion losses. 85% is typical; enter 50–100.
Watts are printed on the device label or in its manual.
Your result
Enter the battery capacity and the device power to see the run time.
Run time = battery Wh × usable % ÷ device watts. Figures are estimates: actual run time varies with temperature, battery age and how the device is used. Fridges, freezers and other compressor loads switch on and off, so in practice they usually run 2–3 times longer than shown. Motors and compressors also need a short surge to start.
How the maths works
Run time (hours) = (battery Wh × usable %) ÷ device watts
Worked example. A 12V 100Ah battery holds 12 × 100 = 1,200Wh. At 85% usable that is 1,020Wh. A 60W device therefore runs for 1,020 ÷ 60 = 17 hours on a full charge. Used four hours a day, that is about four days between charges.
Fridges, freezers and other compressor loads switch on and off, so they usually run two to three times longer than the formula suggests. Motors also draw a short surge when they start, which is why a battery’s maximum output matters as well as its capacity.
Comparing our portable units? See typical appliance run times on the PES 2000W, PES 3600W and PES Lite side by side
Need help choosing a battery?
Tell us what you want to run and for how long, and our Uganda team will recommend the right unit.