The voltage of a car battery can vary depending on whether the engine is off or running. When the engine is off, a fully charged car battery's voltage will measure 12.6 volts, which is known as "resting voltage." When the engine is running, the battery voltage will typically rise to 13.5 to 14.5 volts, and this higher level is maintained by the alternator

. A healthy car battery tested while actively running should read between 13 volts and 15 volts

. A freshly charged battery will be around 13 volts and will settle to around 12.4 volts after being disconnected from charging

. In general, a good car battery should read 12.4-12.9 volts when the car is off