Tools

12 V Battery Voltage Check

Read what your 12 V battery voltage means: state of charge at rest, voltage while starting and the charging voltage with the engine running.

On this page

Tool

Voltage at rest (V)Lowest voltage while starting (V)Voltage with engine running (V)

State of charge at rest
Voltage at rest	State of charge (approx.)
12.65 V or more	100 %
12.45 V	about 75 %
12.24 V	about 50 %
12.06 V	about 25 %
11.89 V or less	discharged

For 12 V lead-acid starter batteries (flooded, EFB, AGM). Not for lithium 12 V batteries or the high-voltage battery of hybrid and electric cars.

How to use it

Measure with a multimeter at the battery terminals. Rest voltage: engine off for at least an hour. Cranking voltage: lowest reading while the engine starts. Running voltage: engine idling with lights and fan off. Enter the values you have.

How it is calculated

Rest voltages follow the open-circuit voltage table for 12 V flooded lead-acid batteries at about 25 °C published by Battery Council International (BCI); AGM batteries read about 0.1 V higher. A healthy battery should stay above 9.6 V while starting (BCI load test). A conventional alternator usually charges at about 13.5–14.8 V; cars with smart charging can show lower values for a while. The maker’s figures always come first.