A typical car battery is a 12-volt battery, composed of six cells each producing about 2.1 volts, resulting in a fully charged battery voltage of approximately 12.6 to 12.8 volts when the engine is off (resting voltage)
. When the engine is running, the car's alternator charges the battery and increases the voltage to about 13.5 to 14.5 volts
. Here is a summary of car battery voltages:
- Fully charged, engine off: 12.6 to 12.8 volts
- Engine running (charging): 13.5 to 14.5 volts
- Below 12.4 volts: battery may fail to start the car
- Below 11.8 volts: battery is considered discharged or dead
Thus, while nominally called a 12-volt battery, the actual voltage varies depending on charge state and whether the engine is running.
