3 hours in the background seems a lot to me.
I started the app clean and configured it from the start (it was a pain in the ass because I migrated my settings from Sync for Reddit lol) and the issue still remains, having this huge background usage prevents my phone from going to deep sleep properly which lends to a bigger battery drain.
EDIT: BTW the issue is gone when I set the app to restricted battery mode instead of optimized... But I'd rather keep it in optimized as it closes less often in the background, that is how I had it with Sync for Reddit, which on average its active background was several minutes only.
EDIT 2:
This is the process that Battery Guru/BBS says shows
job/io.syncapps.lemmy_sync/androidx.work.impl.background.systemjob.SystemJobService#9188
I have an S21 with Android. Sync runs in the background but it doesn't use much power. It looks like about an hour or so of use each day accounts for about 5% battery drain, including background activity, and not including power used by the screen or other services running in the background.
Just a thought though - maybe Sync is making tracking attempts in the background? I recently started using Duck Duck Go's free VPN which blocks tracking attempts made by apps. Some apps, like Messenger and Robinhood, make thousands of tracking attempts every day, even when the apps are closed and not in use. Google makes tracking attempts through Sync, but I've only seen these occur while I use the app. I figured the attempts are made each time an ad loads, but I could be wrong.
It is not that Sync drains too much battery, what is going is that hinders the phone to go to deep sleep which lends to a bigger battery drain, usually my device drains less than .60%/hr without background activity on my part, with Sync for Lemmy with the optimized profile it is always above 1%
This seems like a possibility since I'm always using the AdAway rooted version...
Perhaps Tracker Control might help me to point out something odd there.