A fully charged car battery should have a voltage of about 12.6 volts when the engine is off, which is called the resting voltage. When the engine is running, due to the alternator charging the battery, the voltage usually rises to between 13.5 and 14.5 volts. If the voltage is below 12.6 volts when the engine is off, the battery is not fully charged and may need recharging or replacement soon.
Voltage States of a Car Battery
- 12.6 volts or higher (engine off) : Fully charged battery (100% state of charge)
- Between 12.4 to 12.6 volts : Healthy battery, partially charged
- Below 12.0 volts : Battery is discharged and may need urgent charging or replacement
When Engine is Running
- Voltage should be between 13.5 to 14.5 volts due to alternator charging power.
This voltage range ensures the battery can start the car and power electrical components effectively.
