Why would an alternator charge too much?

Alternators have two parts, one is the armature that generates electricity and the other is a voltage regulator. In most cars the typical output for an alternator is 13.2 to 14.4 volts. If their is more or less than this being produced, the voltage regulator may be faulty or the bushes may be worn.

another issue that some alternators have is the failure of the bearings inside the alternator leading to noisy running or the bearings inside the freewheeling pulley fitted to more and more modern alternators. these can often be replaced independently.