Quote Originally Posted by Bio248 View Post
the battery being dead means that the alternator is doing all the work to keep the car running. without a good battery youre killing the alternator.
Any time the car is running the alternator is what does the work to run the car, not the battery. The reason a dead battery will kill an alternator is because of the extra load the battery places on the alternator as it tries to charge up.

You can take the battery out of a running car and it doesn't care. It's not a load so it doesn't hurt the alternator, and it's not doing anything useful. It just sits there idle until it is needed (like when cranking, or running accessories or something when the engine isn't on).