Solar & battery
Solar Battery Discharge Time Calculator
How fast a battery empties at a given load, and what a high discharge rate costs in usable capacity.
Result
Lead acid delivers measurably less capacity as the discharge rate rises, an effect described by Peukert's law, and the approximation used here is deliberately mild. Lithium iron phosphate is far flatter, which is part of why it outperforms its nameplate comparison with lead. Cold weather reduces capacity in both.
Get a Free Business AuditQuestions
About this calculator
Why does lead acid lose capacity when drawn hard?
The chemical reaction cannot keep up at the plate surface, so the effective capacity falls. A 100 Ah lead acid battery discharged in one hour may deliver only 50 to 60 Ah.
Does lithium have the same problem?
Far less. It is one of the main practical advantages: a lithium bank behaves much closer to its rating whether you draw it slowly or quickly.
The formula
runtime = usable amp hours / load current
Put this calculator on your site
Free to embed. Paste this where you want it to appear. It stays up to date automatically because it loads from BDEVY.
Please keep the attribution line. It is the only thing we ask in return.
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.