How to tell if alternator bad?
My apu is the only thing power my truck (lights). How do I tell if my batteries are fried or my alternator is bad? (I had a voltage surge today of 15.1 without any of my lights on. I turned my lights on and it went back down to 14.-13.9 then about 15 mins. later it dropped to 12.3 and my apu has been bringing it back up to 13.8 all day.)
Is this a good question?