I've been using OwnTracks for years now with no issues. I disabled battery optimization for it. Granted, I don't have a phone made by a manufacturer that has decided to add garbage to the OS to aggressively kill background apps.
Only annoyance is Android has a thing where it doesn't allow apps that start on boot to automatically start getting GPS data, so on every boot you have to tap a notification to kick things off.
Which phone manufacturer is that? I hate having to remember all the apps I disable battery optimization for. I think I currently have like 5 apps or so.
On my iOS device, according to the battery report in the Settings app, the Traccar client does appear to use about 8% of my battery throughout the day. Google doesn’t show up at all, however, which doesn’t seem correct at all, so I’m not sure Google isn’t doing something to hide its true consumption from the OS.
Google's location scraping felt more bulletproof because they seemed to prioritize it at the OS-level on Android over how normal apps function