Sounds like an alternator. If the serpentine belt, tensioner, and wires/ connections are all good the alt. Is a safe bet. Most any shop and even some parts stores can test the battery and alternator in minutes. Some even offer this service for free.
You should be able to purchase a re manufactured alt for under $150.00.
I would expect to pay that much again for installation. You could also find a shop that will rebuild your current alternator. They tend to be somewhat less expensive.
Good luck and let us know. :)
Tuesday, March 28th, 2006 AT 7:02 PM