Free battery runtime calculator
How long will your backup power last?
Pick your power station or inverter setup. Tap the things you want to use. We’ll estimate how many hours you could get.
No electrical knowledge needed · Free to use · No sign-up
1Choose your backup power
Already own one, or just comparing? You can change it without losing your appliances.
Product photos and ratings from the brands’ websites. Match the exact model and regional version.
Battery details — only if you want to change them
The chosen product fills these in. The loss settings are planning assumptions, not measured runtimes.
If the output limit is unknown, enter 0. For batteries labelled V and Ah: multiply the whole bank’s voltage by its Ah rating to get Wh. Never use kVA as battery capacity.
2What do you want to run?
Tap a picture to add it. Add more than one with the + button. Pictures represent appliance types, not particular brands.
Fridge, freezer and bigger appliances
A fridge or freezer needs more power when starting. An iron or AC may be too much for a small unit.
Your appliance list is empty. Tap a picture above to start.
We use example power figures. For a closer estimate, open “Power used” under an added appliance and enter its measured watts or label rating.
3Plan your backup time
We assume everything on your list runs together, with no solar or mains charging. Battery-level options are rough estimates.
See my estimate ↓Battery runtime: enter your own figures
Set battery energy, average load, usable capacity, conversion losses and the running output limit directly. Startup surge, solar sizing and recharge time are not modelled.
About 6.8 hours
1,000 Wh × 90% ÷ (119 W ÷ 90% + 0 W). Compatibility has not been checked.
Simple to use. Clear about the estimate.
This tool estimates battery hours; it does not certify an installation or guarantee that a motor will start. A load below the listed output limit still needs the right sockets, voltage and starting capacity.
Where the numbers and pictures come from
Product capacities, rated outputs and photographs come from the itel, EcoFlow and BLUETTI sources linked beside your selection, checked 23 September 2026. Match the model, region and base battery configuration; boost modes and optional extra batteries are not included. The installed inverter setups are labelled examples, not tested products or recommended installations.
Appliance pictures are illustrations. Their starting wattages are editable planning examples, not measurements or claims about every appliance of that type. Fans vary with speed; laptop and phone charging varies as the battery fills. Fridge/freezer watts describe continuous running, not a measured 24-hour average.
How we calculate the hours
Hours = nominal battery Wh × usable fraction × starting-charge fraction ÷ (appliance watts ÷ efficiency + extra idle watts). The starting-charge multiplier is a simplified approximation, not a model of the battery’s reserve cutoff.
Portable defaults use 90% usable capacity and 90% assumed conversion efficiency, except Power Tank which uses its stated maximum of 88%; actual efficiency varies with load. Lead-acid examples use 50% usable capacity, 85% efficiency and 10–15W extra idle draw. The lithium example uses 90%, 90% and 20W. Change these to match your equipment; do not count losses twice.
Lead-acid discharge-rate effects, solar charging, compressor cycling and starting surges are not calculated. We round estimates to avoid false precision. See Victron’s battery-capacity explanation and inverter idle-consumption specifications for technical background.
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By Bankole Emmanuel · Updated 23 September 2026. Your selections stay in this page and are not saved or submitted. Report a problem.