Backup battery sizing calculator

Tick what you want to keep running in an outage, adjust hours, and get the real kWh you need. For the best result, measure each appliance with a plug meter first.

How this works

We add the watt-hours of every appliance you tick (watts times hours), scale by the days of backup you want, and divide by the usable share of the battery, since you rarely drain a battery to zero. The result is the capacity to look for. Startup surge on fridges, pumps and compressors also matters; check a unit's surge rating, not just its capacity.