Battery Life Calculator
Estimate battery runtime from capacity, load current, depth of discharge, and system efficiency.
Estimates are for planning only. Actual runtime varies with temperature, battery age, and the Peukert effect. Verify sizing with a qualified electrical professional.
How it works
- 1Enter the battery capacity in amp-hours (Ah) and the steady load current.
- 2Set the usable depth of discharge — 80–90% for lithium, ~50% for lead-acid.
- 3Adjust system efficiency for inverter/wiring losses; the result is in hours, days, and minutes.
Use cases
- Sizing a battery bank for an off-grid solar system or RV.
- Estimating UPS backup time for servers or networking gear.
- Checking how long a marine or trolling-motor battery lasts at a given load.
Frequently asked questions
How is battery runtime calculated?
Runtime (h) = capacity (Ah) × depth of discharge × efficiency ÷ load (A). A 100 Ah battery at 5 A with 80% DoD and 90% efficiency gives 100 × 0.8 × 0.9 ÷ 5 = 14.4 h.
What depth of discharge should I use?
Lithium (LiFePO4, Li-ion) can be discharged to 80–90% without much wear. Lead-acid (flooded or AGM) should be kept to ~50% to preserve cycle life.
Why does actual runtime differ?
The Peukert effect reduces usable capacity at high discharge rates, and cold temperatures and aging cut capacity too. Use the estimate for planning, then test in practice.
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