I unplugged and replugged the charger instead of only checking the cables of the Asus docking station.
And I ran advanced task killer, killed a bunch of apps.
After this it began to charge really quick, as I was used to it.
Now the battery is as 100%
shows 4.179.000 µV
Which is the same as the app "akku&batterie hd" by smallte.ch reports.
So if I can exclude a hardware error, some software must have caused it.
But my highest usage shows "display" that caused 73% of the drain.
32Gb Nexus 7 - grouper
HTC Touch Cruise with Windows Mobile 6.1