A fully charged 12-volt automotive battery should have an open-circuit voltage of:

A fully charged 12-volt automotive battery should have an open-circuit voltage of approximately 12.6 volts. This value is indicative of a battery that is in good condition and fully charged. The open-circuit voltage is measured when the battery is not connected to any load or charger, which provides an accurate reading of the battery's state of charge.

Typically, a starting lead-acid battery reaches its full charge at around 12.6 to 12.7 volts. If the voltage falls below this range, it may indicate that the battery is not fully charged or is undergoing some form of deterioration. At 12.3 volts, the battery is about 75% charged, and at 12.0 volts, it is roughly only 50% charged. Measurements higher than 12.7 volts (like 12.9 volts) could indicate overcharging or surface charge, which is not the desired normal operating voltage for a fully charged battery.

This understanding of battery voltage is crucial for diagnosing battery health and ensuring that the vehicle's electrical systems operate efficiently. Keeping the battery fully charged also extends its lifespan and performance capabilities.