Yesterday, I was able to finally see the pattern that triggers the battery draining. I used the phone in the same way as other days, however there was a short phone call in the morning. After it the battery just went down. Phone reboot fixed the problem as it is visible on the battery usage.
Is any Samsung person able to comment on this if a fix is coming? Rebooting phone after a phone call is just crazy! Thanks!
After yet another night of 15-20% battery decrease and no app reported as the battery drainer, I went over apps via "Apps" and noticed couple of Samsung apps with the same metrics:
Surely, Device Care app should not consume 10% over 8 hours when phone is not used.
I found something that might help figuring out why the battery is draining faster than expected. The first sceenshot below shows battery usage over time, together with CPU Utilization % and CPU average frequency.
Note that for the whole of Sunday, CPU utilization remained close to 100% and CPU frequency was almost constant until I restarted my phone (as indicated by the gap in the data). After this point CPU utilization varied normally and only increased when the phone was actually in use.
It's seems that the abnormally high CPU utilization caused the battery to be consumed much faster than expected. In the second screenshot this is clear as indicated by the steep slope for battery usage compared to the much flatter slope after the restart.
It is also worth noting that this high CPU utilization has been persisting for more than a day and throughout a charge before I noticed it, so it may be the case that a restart is necessary to fix the issue.
@VincentKen I checked and this increase in CPU usage was not triggered by a phone call in my case.
I suspect that it must be some system process that is causing this issue, since no app is indicated as the culprit in the battery monitor or in Gsam.
