Use this electronics calculation for a first-pass component, converter, signal, motor, or sensor estimate when the stated operating conditions and units match the device data.

Open-circuit voltage (V)

Terminal voltage with no load attached.

Loaded voltage (V)

Terminal voltage while supplying the load.

Load current (A)

Current drawn by the load.

Estimate battery internal resistance from open-circuit voltage, loaded voltage, and load current. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Internal resistance (Ω)

Equivalent series resistance of the battery.

• Battery capacity, state of charge, runtime, and aging depend on chemistry, temperature, discharge profile, cutoff voltage, cell balance, charge method, rate capability, self-discharge, and prior history. Nominal amp-hour or watt-hour ratings do not guarantee usable energy under every load.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check the result against the current datasheet and worst-case operating corners, then verify the circuit or measurement with simulation and bench testing where failure matters.

• Battery Internal Impedance

  Estimate DC battery internal resistance from the voltage drop between two load-current operating points measured over a short interval.

• Battery Life Calculator

  Estimate battery runtime from rated charge capacity and constant load current: hours = mAh / mA. Real-world derating (Peukert effect, temperature, cutoff voltage) is not modeled.

• Fuel Gauge SOC From Voltage

  Estimate fuel-gauge state of charge by linear interpolation between user-supplied empty and full open-circuit voltages; chemistry, load, and temperature can make this inaccurate.