To everyone who is following this thread: These tips might help you have more capacity again!
[quote=“Stefan,topic:5372,post:7”]At FP they told me that the battery has its own software inside, which sometimes needs to be reset.
- Use the battery up until it is below 0% (until the phone dies).
- Take the battery out of the phone.
- Plug your charger into the phone (still without battery).
- Insert your battery. (This will give the battery a kick)
- Charge your phone in one go until 100%. Do not boot.[/quote]
Edit: It works for me! 
I get through the day easily again! Edit2: You might need to follow the procedure multiple times to notice a significant improvement of the battery’s capacity.
If you have a bloated battery you should contact support immediately. A bloated battery is dangerous because it can burst!