Just went through this whole topic, since I also have this battery drain and heating issue on PA 836.
I mostly use PA while out riding the motorcycle, so my Galaxy S7 (android 8.0.0) is connected to my Sena 3S headset, while the phone is mounted on the bike with the screen turned off.
I have a 2 hour drive going home on Friday and back on Sunday, so that is when I use the app for a longer period.
Last Friday going home, the phone was at about 90 percent charge when I left and after two hours listening to music and using Flitsmeister navigation (screen off, only notifications through headset), it was at 65%. What seems to be oke.
And leaving home yesterday, the phone was fully charged, using Flitsmeister and Poweramp again, it died after less than 2 hours.
The difference was Friday I had a playlist that only had 16bit 44.1KHz Flac files, yesterday it was all 24bit 96KHz.
I'm going to install the build without google services and try again this week.
Does build 838 have Google services?