@moodroid The “Prevent background suspension” setting should be set to OFF. As described in the Ubuntu Touch Wiki.
By “Power Save,” I mean the following:
Set CPU cores to half load
Turn off Wi-Fi
Turn off mobile data
Turn off Bluetooth
Turn off location services
Enable 2G (optional)
With these settings, the device enters deep sleep mode and consumes less than 22 mA. (1-2% battery consumption at night) If this is not the case, you will need to check for faulty services or configurations that are preventing deep sleep mode. In my case, I created a script with a log file that records the power consumption of the idle device in a text file. It was always over 200 mA. Only after cleaning up faulty services linked to installations did the consumption drop to ~22 mA.
The battery on my 9-year-old Pixel 3a now lasts about 4 days with moderate use. I call it “NOKIA 3210 mode.” You can be reached via text and phone for days on a single battery charge. If needed, you can also take pictures, check emails and calendar events, send texts, or make calls, and all other features of a modern smartphone are available. (Navigation, internet, NextCloud, cloud music...)