Parked my 06ss Friday didn't drive it Saturday, took it out Sunday turned over slow and got a "service brake assist" message, but started and ran fine. Got in to go to work Monday everthing was dead. Interior lights were barely on when I opened the door, took 45 minuted to just start it. waited 2 hours for GM roadside assist to get someone there. Would have done it myself but I figured I would let GM pay for it.
Took it to nearest dealer (150 miles from my usual one). They tested it and found no problem but decided to keep it overnight just to make sure. They called yesterday and said the battery was losing more than half of its CCA no unusual power drain. New battery and while it was there replaces the Keyless remote module and antenna, ordered new fobs.

I haven't seen a battery go bad that fast. They gave me a POS 06 Cobalt to drive. Not real happy with giving them a 30G car and getting a 12G car as a loaner. Alls well with the Monte so far but just picked it up last night. Anyone else have a new battery tank that fast?

 

I did in my 04, but it was because it sat for a long time before I got it. The new replacement battery has been great though.