Battery Runtime & Charge Calculator

Estimate how long a battery will power a load and how long it takes to recharge. Enter the battery capacity (in mAh or Ah), nominal voltage and a usable-fraction derating to get watt-hours; then enter the load (in watts or amps) for the runtime, and the charge current and chemistry for the charge time. Useful for UPS sizing, drones, portable electronics and off-grid power. The usable fraction reflects the part of the rated capacity you can actually draw before the cutoff — pure arithmetic, not a real discharge model. Everything runs locally in your browser.