Check your serpentine belt for excessive looseness, or perhaps a major oil leak that might have caused it to slip on the alternator. After you do that, clean your battery posts and terminals nice and shinny with a combo wire brush cleaning tool for batteries, and conduct all of Larry's tests.... BTW, changing the brush holder- Voltage regulator module might bide you some time instead of a RB or new alternator, but those brushes ride a commutator disc thats part of the armature. if the commutator is shot, its time for another unit.....

Dave....