How the calculation works
Energy to back up = load × hours. Battery size = energy ÷ (usable depth of discharge × inverter efficiency). Amp-hours = battery size ÷ voltage.
Frequently asked questions
Lithium or lead-acid?
Lithium batteries usually allow deeper discharge and last longer, but cost more.
Should I add a safety margin?
Yes. Add 10 to 20% for ageing and unexpected loads.