Battery Internal Resistance Calculator
How much voltage does the battery lose inside itself under load?
Measure the resting voltage, then the voltage at the terminals with a steady load running and the load current. Everything is worked out in your browser. Nothing is saved or sent anywhere.
1. Readings
2. Results
How it was worked out
What this does and doesn't tell you
- Measure right at the battery posts. Cable and connection resistance adds to the result.
- Internal resistance rises as batteries age and when they're cold.
- 240V AC mains can kill. In Australia, work on household mains wiring must be carried out by a licensed electrician. Low-voltage DC systems can still deliver very high current.