I got my battery fixed now, and I didn't even had to go to the Apple store. A day after my call a very friendly technician called me back, asked for a couple of information (battery cycles and so on), and in the process it turned out that, for some reason, the dock application was running and took out about 90% (?, but that was what it said in the activity monitor) of the processor power. No wonder that drained the battery.
However, with some guided instructins over the phone and some lines in a console (i forget the name of that), the process was shut down, and even though the dock immediately reapeared, it now does not use that much processor power anymore, resulting in almost the advertised battery life.
I don't want to sound like a fanboy, but I have to say I am very pleased with the support. Thank you!