Since the voltage level is determined totally by the battery and the alternator, and it is not possible for the battery to produce more volts that we need because of the material it is made of, the alternator had to be the culprit.
That is because the voltage level is regulated and produced within the alternator unit itself. Of course, the alternator has to be replaced and the excess voltage will not exist. All that is left to do in "clean up the mess"
So sorry...