Most people shopping for backup power start with the battery, then work out what it can run. Doing it the other way around is cheaper: decide what has to stay on, then buy the smallest battery that covers it.
Use the calculator below to add up what you need. It checks both the energy (kWh, how long things run) and the power (watts, including the startup surge from motors like fridges and sump pumps), then matches you to the power stations I have reviewed.
Battery Backup Calculator
How big a backup battery do you need?
Tick what you’d want running during an outage, pick how long, and see which power stations can handle it.
Estimates use typical wattages and assume about 85% of a battery’s rated capacity is usable after inverter losses. Check your appliances’ labels for exact numbers. 240V loads like well pumps and central AC need a whole-home system and aren’t covered here.
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