A fully charged car battery should have a resting voltage of about 12.6 volts when the engine is off. This is considered the normal and healthy voltage for a standard 12-volt car battery. When the engine is running, the battery voltage should rise to between 13.5 and 14.7 volts due to charging from the alternator. If the battery voltage drops below around 12.4 volts when the engine is off, it indicates the battery is not fully charged and may be losing capacity. During engine start, the voltage can momentarily drop to around 10 volts due to the high current demand. In summary:
- Engine off (resting): about 12.6 volts (fully charged)
- Engine running: 13.5 to 14.7 volts
- Engine starting: around 10 volts (momentary drop)
Maintaining the battery voltage near 12.6 volts when off is important for optimal car battery health and performance.
