a friend of mine owns this Galaxy S9+. The device had been stuck to /e/OS 2.6.3-s, so I upgraded manually without clearing /data.
Since then she needs to charge the battery twice a day (in comparison to every second day before the upgrade). The battery usage panel shows, that it’s “Android-System” which is consuming significantly most of the power.
Restricting Android-System to “limited battery usage” did not help.
In case it does not work well on your system (in my experience and despite closely following all the instructions it sometimes behaves awkward on newer android vetrsions) you may as well use SD maid SE (“function is called app cleaner”)
I have a S9+ too. Hven I updatet to 2.2 my battery time vent from 6 days to 48 hours.
The last week I have placed my phone on the table with the screen downwards.
Now my battery time is 6 days.!!!?
I dont now why, maybe some sensor shut down some processes.