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.