Just a story - my Chevy one day no radio or sat nav, dash display weird - dealer says need new battery - car not very old - spoke to Chevy customer service - have you been away for a while and not used it, me yes - its gone into powersave mode so shuts down things it doesn't need, the dealer should have known because that's what they do when they are in showroom or stock. Replacing battery would have fixed it, but so did the instructions Chevy gave me without buying a battery. Try other things first.

Oh by the way not a peep out of my Crossfire since lifting tailgate the other week and no new battery