I've done the following steps and it seems to work for me:
- Charge the phone to 100% until there no charge indicator left
- Boot the phone to bootmenu (where you can select recovery, fastboot, etc.)
- Leave the phone in this bootmenu until the battery is empty (in my case this took 8-9 hours)
- Charge the phone until there is no charge indicator left
After these steps my E4.5 lasts almost as long as it was new and the percentage shown in the power-management shows the correct values again.
I hope this is a long-term solution.