I was off both working and partying all day, glad Steve got the tech theory out of the way for you, he's great at that.
The brushes on the old one really looked shot alright. The picture I would really need to see is the tips of the 2 brushes, where it contacts the rings. Usually, one of them will look really dull, and the other will be shinier, as usually one fails first and the other still makes contact. Have any problem getting it installed?
Your battery should be just as good as it was before, the alternator will charge it up just fine now.