My 2013 CTS coupe, with 14,000 miles, had a very dead battery that possibly triggered the code of bad alternator. Indie garage guy that I’ve used before put in a new battery and said the computer shows I need a new alt. He could install it for $950.00! I couldn’t believe it needed replacing so i said no thanks, just the battery. That was 6 months ago and no electrical problems since. Was he trying to rip me off?