A car battery's voltage should be:

• With the engine off: Ideally between 12.4 and 12.7 volts , with a fully charged battery typically reading about 12.6 volts. This range indicates the battery is healthy and has enough charge to start the vehicle

• With the engine running: The voltage should be higher, between 13.7 and 14.7 volts , which shows the alternator is properly charging the battery while the engine operates

• Below 12.4 volts (engine off): This suggests the battery is partially discharged or weak and may need recharging or replacement soon

• Above 12.8 volts (engine off): This could indicate overcharging, which can damage the battery over time

For accurate voltage measurement, it’s best to check the battery after the car has been off for at least 15-30 minutes to get the "resting voltage" reading

. In summary, a healthy car battery should rest around 12.6 volts when off and show between 13.7 to 14.7 volts when the engine is running to confirm proper charging