Pontiac G8 GT 2009.5 E38 ECM - Flashed with no errors, car will not start

OK folks, I'm new to all this so bear with me...

Took my G8 in to have inspection done last week, they complained that O2 heater and EVAP weren't showing readiness codes because I'd recently flashed it while working on my transmission tune. I waited a week, flashed a "DTC all ready" tune into it, car started and ran fine. Drove it to inspection, passed, they mentioned something about the battery looking low which puzzled me because engineering mode showed 68% charge and voltages looked correct.

So I start it, drive a while to make sure battery has a good charge, and I stop to flash in the new tune I wanted to do. It flashes in with no errors, so all looks normal procedure until I turn the key off and then back on to start the car. Oh boy, it won't start, it will barely even turn over, and the BCM is acting like it's freaking out because the radio wants to come on when it shouldn't etc.

So I figure maybe it needs to sit for a while with the negative battery terminal unplugged. Which is what it's doing at the moment. Any ideas where I may have gone wrong and screwed up? I know y'all probably see dumb posts like this all the time but any help is appreciated.

Jump it. Your battery is weak.

Bingo, you are correct DSteck... tested the battery, it showed as "weak", and since I know the G8 is notorious for hating weak batteries I ripped it out and replaced it... fired up like it was nothing, problem solved.

Good to know, Thanks guys. My GF pick up a 2009 G8 GT a couple months ago.

snowvette, this is why I won't run an underdrive pulley on a G8... the car is just too picky when it comes to all the juice needed to run the electronics... this little experience simply reinforces that assessment

edit: data point, I got 55k miles and 5 years out of the factory AC Delco battery before needing to change

My OEM battery last 2 years and left me stranded in my old G8. They seem to be hit or miss.