Sorry, the battery can't cause overvoltage problems.
I refered to the battery thinking that only one cell was gassing. With that voltage they all should be gassing.
BTW after repairing the alternator or regulator, you should be sure the fuse in the overvoltage protection relay isn't blown. Its job is to protect the control units from these kinds of voltages.
Bosch Master, ASE Master, L1
33 years MB technician