A fully charged car battery should have a resting voltage of about 12.6 volts when the engine is off. When the engine is running, the voltage typically rises to between 13.5 and 14.7 volts due to the alternator charging the battery. Voltage readings below 12.4 volts indicate the battery is not fully charged, and if it drops below 11.9 volts, the battery charge is quite low and may not start the car reliably. For accuracy, voltage should be measured after the car has been off for 15-30 minutes.
Car Battery Voltage States
- Fully charged (engine off): ~12.6 volts
- Healthy charge range (engine off): 12.2 to 12.6 volts
- Charging voltage (engine running): 13.5 to 14.7 volts
- Voltage below 12.4 volts (engine off): battery not fully charged
- Voltage below 11.9 volts (engine off): low charge, likely battery issues
These values apply to standard 12-volt car batteries and good battery maintenance includes regular voltage checks to ensure proper charging and health.