How old is your battery? I was told several times my battery was fine too, until it died without warning. Gave it a full charge, and later that day it died again. I replaced it and that cured the problem. I’ll agree with what others are saying too about a parasitic load draining it.

I saw my first failed closed thermostat that caused overheating when I was 12…1967 Pontiac Executive. I’ve seen many more since. I don’t blame you for being gushy about out this mechanic.

And this is why I cringe anytime I have to take a car to the dealer.

Unless there’s any indication of problems, go timeout local auto parts store, buy the two air filters and replace them yourself. The rest of the stuff, forget it. I had a Chevy dealer want to charge me $495 to replace the brake fluid on a two year old Sonic.