If you end up having more problems, I'd ask the dealer if they had performed a parasitic drain test. How it is done is you put a multimeter in series with the battery and check the drain on the battery with the car off.
Each car has a certain amount of draw for things like keeping your radio presets, etc. It was my experience when I used to work on GM products, that the manufacturer states a normal draw in amps. Anything above a certain amount and you have something "on" that shouldn't be.
I've seen bad trunk switches for example causing the problem. The switch wasn't closing all the way and the trunk light was staying on. You wouldn't know it because the trunk is closed.
How you find the problem is to start pulling fuses. When you see the amps drop down to where the should be, you know that the problem is somewhere in that circuit assigned to that fuse.
Here is a link explaining the same thing. Perhaps better than I am.
http://www.autoshop101.com/trainmodu...rvice/118.html