David,

I suspect that your alternator is going bad. If the pulley is not pulling I mean let's think about this logically. If the belt is tight and it's turning, then it should turn the alternator. If your battery is not charging then it's your alternator.

Before spending a bunch of money at a dealer I would buy a new alternator, install it then see for yourself. If, in fact, it's not the alternator return it.

Jonathan