After a week of excellent battery performance, the problem is back. After I switched to 2g mode and had 3 full days of battery, I figured I'd install a few apps. I got jeweled, puzzle collection and mancala and I updated my fm radio (just installed not played).
That was yesterday with a fully charged battery. This morning I woke up to the beep of low battery and by the time I got out of bed the phone shut down.

CPU and Mem usage are close to zero, no active connections, no background applications running...

I am now pretty sure that something goes wrong when I install a new app or udate an existing one. I can't explain it otherwise...