Do you know how to tell whether the battery is fully charged?

After we charge the battery with the charger, remove the charger and test the voltage of the battery with a multimeter. At this time, the battery voltage should be higher than 13.2V, and then let the battery stand for about an hour. During this period, the battery should not be charged or discharged.After one hour, use a multimeter to test the battery voltage. At this time, the battery voltage should not be lower than 13V, which means that the battery is fully charged.

* Note: Do not measure the voltage of the battery when the charger is charging the battery, because the voltage tested at this time is a virtual voltage, which is the voltage of the charger, and cannot represent the voltage of the battery itself.