Battery Life Calculator

Turn battery specs into practical runtime and sizing. Compare chemistries, discharge rates, and margins safely. Get clear results fast, then share them with teams.

Calculator Inputs

Choose a goal, then enter battery and load details.

Battery Specifications

Rated values at 25°C unless specified.

Load Specifications

Provide power in watts, or current in amps. Duty cycle models intermittent operation.
For direct DC, this is battery-side current.
Covers wiring, DC-DC conversion, regulator loss.

Discharge Limits & Derating

Tune DoD, reserve margin, temperature, aging, and discharge behavior.
Kept unused for uncertainty and peak events.
Capacity remaining due to aging or prior cycles.
Advanced discharge modeling (Peukert & rated hour)
Most relevant for lead-acid at higher currents.
Common datasheet rating: 20h for lead-acid.

Target Runtime

Used only when sizing a battery.
Tip: For intermittent loads, set duty cycle to the average on-time percentage.

Example Data Table

Scenario Voltage (V) Capacity (Ah) Load (W) DoD (%) Reserve (%) Estimated runtime Hours
Portable sensor kit 12.8 100 60 90 10 16 h 25 m 16.42
Telecom backup 12.0 200 150 50 15 6 h 28 m 6.46
Mobile workstation 24.0 40 120 80 10 5 h 28 m 5.47
Examples assume 25°C, 100% health, 100% duty cycle, and 95% DC efficiency.

Formula Used

The calculator converts rated capacity into usable capacity, then divides by average load.

  • Wh = V × Ah
  • Pterminal = Pout / (ηinv × ηdc) (when inverter is used)
  • Iterminal = Pterminal / V
  • Iavg = Iterminal × duty
  • Aheffective = Ah × fPeukert × ftemp × SOH
  • Ahusable = Aheffective × DoD × (1 − reserve)
  • Runtime (h) = Ahusable / Iavg

Peukert uses fPeukert = (Irated/Iavg)k−1 with Irated = Ah / hour-rate.

How to Use This Calculator

  1. Select Estimate runtime or Size for target runtime.
  2. Enter battery specs as a pack, or build from series/parallel cells.
  3. Choose load path and enter power or current.
  4. Set duty cycle and efficiencies to match real conditions.
  5. Adjust DoD, reserve, temperature, and health for safety margin.
  6. Press Calculate and export results using CSV or PDF.
Engineering reminders
  • Inverter surge and motor starts can exceed steady power.
  • Battery voltage sag can trigger early cutoffs in equipment.
  • Use manufacturer curves for best accuracy at cold temperatures.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.