Calculator
How long a battery runs a load
Estimate how long a battery can run a given load, based on usable capacity for the chemistry and typical inverter losses.
Related calculators
Usable capacity after depth-of-discharge
Daily watt-hours for a device
How many days your battery bank lasts
Looking for a definition or a quick answer? See the solar & battery glossary for terms used on this page, or the FAQ for common sizing questions.
Sources & standards
- IEEE 1013 — Recommended Practice for Sizing Lead-Acid Batteries for Stand-Alone Photovoltaic Systems — Widely used engineering practice for days-of-autonomy and depth-of-discharge sizing methods, referenced here for the general sizing approach.
- Victron Energy — Battery Capacity and the Peukert Exponent — Manufacturer technical explainer on why usable capacity falls at higher discharge (C-)rates.
- UL 1973 — Batteries for Use in Stationary and Motive Auxiliary Power Applications — Safety standard most LiFePO4 and other stationary/portable battery packs are certified to.
Estimates for planning only. Verify with a meter and follow NEC / local code; have a licensed installer confirm any system before purchase or wiring. See the methodology for formulas and sources.