And so I wondered if it now would not be the time to just buy a brand new toothbrush.
New game new luck.
The installation is not for people with no knowledge and no electric hand skill with a fine soldering iron. The toothbrush is opened by turning up very carefully on the charging station. And then you have to push out the inner workings. The battery must be soldered.
But the effort of 15 minutes has been well worth it this time. Charging runs downright. The charge is held literally. The toothbrush runs and runs and runs.
I can of course make no statement about the lifetime of the battery. But for now I am very satisfied.
Supplement 03.19.2014: A deterioration of battery performance, I have not yet noticed.