"...or even de-Googled Android, on a normal Android device can absolutely tank your battery life."Not necessarily. About eight hours ago I was having trouble with the GPS on my main phone (I cleared GNSS on GPStest app and it wasn't refreshing fast enough), so I found another in my assortment of phones that was still running and had some charge left in it and used it (it also had GPStest installed)—and I'm using it now to post this comment.
It's a Huawei GR5 Honor from 2017 with original battery that I've de-Googled, and when I picked it up earlier the battery indicated 22℅ remaining which surprised me because I've not used it for some weeks.
When I read your comment I thought I'd ckeck the battery and phone usage logs and I'm now even more surprised. The phone was last used on July 19 (24 days ago) and the battery drain graph shows a very gentle and almost perfectly linear decline from then (until I put it on change and started using it).
Moreover, it estimates remaining battery life in standard/default power mode at 8 days 23 hours (but it's since been on change). Note: the phone was set to standard power mode during those past 24 days. If I switched to 'Power Saving' mode the estimate is 11 days 16 hours, and in 'Ultra Save' its estimate is nearly 33 days (778 hours 44 mins).
Incidentally, the phone has 346 apps installed.
It's amazing what battery life one can achieve when one stops both Gapps and user-installed apps yapping back to Google-Central.