Battery life calculator
Enter capacity and load. Add depth of discharge for lead-acid or LiFePO4 banks, inverter efficiency for AC loads, or a duty cycle for devices that sleep between readings.
Best-case estimate. Real capacity falls with high discharge rates, cold, and age.
How runtime is estimated
Runtime (h) = capacity (Wh) × usable fraction × efficiency ÷ load (W)Working in watt-hours lets you mix units: a 100 Ah, 12.8 V LiFePO4 battery holds 1,280 Wh; at 90% usable and through an 88%-efficient inverter it runs a 150 W load for 1,280 × 0.9 × 0.88 ÷ 150 ≈ 6.8 hours.
For sensors that wake briefly, the average current matters: 20 mA for 2 s every 60 s plus 50 µA asleep averages about 0.72 mA. A 2,000 mAh cell then lasts roughly 115 days.
Questions people ask
How do I calculate battery life?
Runtime (h) = capacity (Ah) × usable fraction ÷ load current (A). A 2,000 mAh battery at 100 mA lasts about 20 hours before derating.
How much of a battery can I use?
Lead-acid batteries last longest when discharged no more than about 50%. LiFePO4 is commonly used to 80–90%. Check the manufacturer’s cycle-life data.
Why does my battery run out sooner?
Capacity falls at high discharge rates (the Peukert effect, strongest in lead-acid), at low temperature and with age. Treat the result as a best case.