Work out battery capacity (ah) instantly with clear inputs, formula shown and shareable results.
Required capacity is load current times hours, divided by the usable depth of discharge and again by an ageing and temperature derating. Depth of discharge is the big factor: a lead-acid bank limited to 50% DoD needs twice the nameplate capacity of the raw amp-hour demand.
Battery sizing
Ah = load x hours / DoD / (1 - derating)
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.
Around 50% for flooded lead-acid to get reasonable cycle life, 80% for AGM in light service, and 80-90% for lithium iron phosphate.
Available capacity drops roughly 20% at 0 degrees C and much more below that, while high temperatures shorten life.