99 jetta battery problems

I've replaced the battery twice since I bought this car new. It went dead in december and I got it checked out by the VW dealer. I also was having driver side door lock problems (it wasn't locking, all the other locks locked). Anyway, they said they couldn't replicate the problem. Spent $200 on their services and actually didn't have those problems until now (May). I originally thought it might be a cold weather issue, but it's like 85 degrees outside. I also assume the door lock and battery are related because they both arise the same times. I triple check my car to see if I leave any lights on, but nothing. I turn off everything (ie: radio) before i turn off the engine.

Now the car hasn't died this time yet, but everytime I try starting it, it hesitates. Except, if I was just driving the car. It will start up without a hitch. Only when I leave it overnight.

Can't figure out the reason why it's draining. It seems like a lot of new jetta owners have the same problem, but i have not read a solution. except for getting a new battery.

Any ideas? By the way, I don't know anything about cars, except for the pure pure basics of how it runs.