Battery Internal Resistance Calculator

How Battery Internal Resistance works

The arithmetic follows r = voltage drop ÷ test current. Battery Internal Resistance uses Open voltage, Loaded voltage drop at 20 A to report Internal resistance.

With the loaded values, internal resistance evaluates to 0.03 Ω. Isolate a single uncertain input during sensitivity checks.

Inputs for Battery Internal Resistance

Open voltage and Loaded voltage drop at 20 A belong to Battery Internal Resistance. Keep source units with open voltage.

Loaded numbers demonstrate the calculation; they are not equipment recommendations. Replace them with values from the case being evaluated.

Open voltage

Example entry: 12.8 V.

Loaded voltage drop at 20 A

Example entry: 0.6 V.

Reading the Battery Internal Resistance result

This output represents Battery Internal Resistance. If the next question concerns bank capacity, open Battery Bank Capacity Calculator.

The worksheet isolates arithmetic; final ratings need a broader equipment check.

Measurement and units

Battery calculations depend on chemistry, temperature, age, discharge rate, and the limits of the battery management system. Check prefixes on open voltage. Compare this result with Battery Self-Discharge Calculator when capacity remaining is also needed.

Preserve the measurement basis when testing alternatives.

Limits of this calculation

Use a documented test current and stable state of charge. Use Battery Energy Density Calculator as the follow-up for volumetric energy density.

The result reflects the formula scope, not every connected component. Unentered effects remain outside Battery Internal Resistance.

A useful Battery Internal Resistance comparison

Record internal resistance before testing a different open voltage value.

Document the alternate open voltage source.

Battery Internal Resistance record notes

Record source and operating details for open voltage.

Retain raw internal resistance beside its selected rating.

Questions about Battery Internal Resistance