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 Volts (V)

Required number input.

Loaded Volts (V)

Required number input.

Load Amperes (A)

Required number input.

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

The resulting internal ohms returned as a number.

• 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.

• Internal Resistance

  Estimate battery internal resistance from open-circuit voltage, loaded voltage, and load current.

• VCO Tuning Sensitivity

  Average VCO frequency tuning sensitivity between two measured voltage-frequency operating points.

• Contactor Coil Current

  Calculate DC contactor-coil steady current from applied voltage and DC coil resistance; do not use this for AC inrush or inductive impedance.