Pack Internal Resistance Calculator

High internal resistance means sag, heat and short run time.

Measure at the terminals with a known steady load. Don't short a pack to test it. 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

    • Pack rebuilds involve lithium cells that can short, burn or explode. Only work on packs if you have the right knowledge, tools and fire safety in place.
    • Compare packs of the same model at the same charge and temperature.
    • Lithium-ion tool packs can short, overheat and catch fire if they're damaged, wired wrongly or charged on the wrong charger. Only use the maker's charger for the pack.
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