When there is doubt about a voltmeter reading we always suggest first reading battery voltage without the motor running (turn headlights on for 1 minute and then off to remove surface charge). Then measure battery voltage with the motor running at fast idle. Compare the amount of change. 12.5V for good battery and 14.5-15V on a charging battery.
The rule of life at RECONIT: All batteries are guilty until proven innocent by replacement!
The rule of life at RECONIT: All batteries are guilty until proven innocent by replacement!