About Battery Runtime Calculator

Battery Runtime Calculator is a small, independent site with one job: answering “how long will this battery last?” and “what size battery do I need?” quickly and honestly.

Why this site exists

Most runtime calculators online are a single box on a battery seller’s product page. Many skip inverter losses and depth of discharge, and almost none apply Peukert’s law, so they overstate runtime, sometimes by a factor of two for small lead-acid batteries under heavy loads. We wanted calculators that show their working, explain their assumptions, and give the same answer you would get by hand.

How the calculators work

Every calculator uses the same calculation engine: capacity converted to watt-hours, inverter efficiency, usable depth of discharge by battery type, Peukert’s law for the discharge rate, and battery health. The method, formulas and sources are published in full on how battery runtime is calculated, and each result shows its own step-by-step working.

The numbers quoted in our articles and tables are generated by that same engine when the site is built, so the text and the calculators cannot disagree. The engine is covered by automated tests with examples worked out by hand.

Our calculators

• Battery runtime: Runtime for any battery and load, in Ah or Wh, AC or DC.
• Battery life (mAh): mAh and mA to hours, with sleep current and duty cycle.
• Battery size: Hours you need in, battery Ah, Wh and count out.
• Solar battery bank: Daily kWh and days of autonomy to a battery bank size.
• UPS runtime: Backup minutes for a computer, router or NAS on a UPS.
• Inverter backup: Home inverter backup hours for 150 Ah to 220 Ah batteries.
• Power station runtime: Wh rating to runtime for portable power stations.
• 12V battery runtime: 12V deep-cycle runtime for RVs, vans and boats.
• Ah to Wh converter: Amp hours, watt hours and kWh at any voltage.
• mAh to Wh converter: mAh to Wh for power banks, with the 100 Wh flight limit.
• Charge time: Hours to charge from any state of charge, by charger amps.

Independence

We do not sell batteries and no manufacturer has paid to be mentioned. The site is free to use and has no sign-up. In future it may show clearly labelled advertising to cover its costs; ads will never sit between a calculator and its result, and they will not change how anything is calculated.

Privacy

The calculators run entirely in your browser. What you type is not sent to us. Details are in the privacy policy.

Contact and corrections

Found a mistake, have a battery datasheet that disagrees with our defaults, or want a calculator we do not have yet? Email hello@batteryruntimecalculator.com. We read everything and correct errors quickly; the date at the top of each page shows when it last changed.

Disclaimer

Results are estimates for planning. Real runtime depends on the specific battery, its temperature and age, and the actual load. Confirm with the manufacturer’s datasheets before buying equipment, and do not rely on these estimates alone for medical or safety-critical equipment. See the terms of use.