My battery light came on a few days ago. I knew it was time for a change, as it has been nearly 7 years since I last changed the battery out. After the change, the light stayed on.
We tested the alternator voltage and it was only @ 12V

Guess it is time to replace that, too.
It was probably my fault... I'm running my battery / alternator to a 200A relay which feeds into an Optima red top in the truck with 3 subs and 3 amplifiers... I'm actually surprised that the alternator lasted THIS long...
Anyway, the alternator is supposed to be throwing at least 15-16 volts, correct?