Attention:

In order to minimize eventual residual surface charges, consider to leave the radio or headlights on for a couple of minutes prior to the measurement procedure.

Procedure:

1. Set your multimeter to DCV and select a range at least above 15V.
2. Connect the multimeter leads (black is ground) to the battery. The optimal reading is around 12.6V.
3. Now start the car with the multimeter connected to the battery. Voltage should not drop lower than 10V (it’s ok to drop to 11V).
Read more “Debugging your car’s battery and alternator with a multimeter”