I've been killing the battery in my 08 Alpha... it could be the battery, but it's less than a year old, what I'm thinking the problem is is similar to a problem I had with a 06 GTO - the computer wouldn't shut off when the ignition switch was turned off. The Alphas, in GM's thought pattern, turn on the computer when you put the key in the ignition. The problem is, if you turn to accessory, the computer stays on for 30 minutes (why, I don't know, I just know this is how it's programmed). Sometimes it doesn't shut off, and eventually just stays on 24/7. It will make your battery dead enough that it won't start after 24 hours. When the GM tech looks at it, make certain he checks for this issue - they HATE checking this stuff because it doesn't pay squat for the amount of work it requires; but perhaps if you get him travelling down the path, it will quickly turn out to be a computer (yep, you have to replace it)....
Don't leave your key in the ignition, and if you're having to pay to fix, pull the relay (71, IIRC) when you shut the car off - then when you go back after 3 days, plug the relay back in - if it starts... there's the issue....
