So I decided to try out KOreader again, used nicklemenu, and the nightly build from 11 Nov (looks like it was pushed on 12 Nov).
https://build.koreader.rocks/downloa...c2_2021-11-11/
I'm sorry if this is fixed now, as there is a new nightly build, or if it's a known issue still being tweaked. But boy howdy is koreader a battery drainer on the Kobo Sage. We're talking 10%+ in under 30mins of reading.
I generally like koreader (in the short time I used it, aside from an issue opening large ebooks, it's nice and I can squeeze the margins just ever so slightly smaller than I can on the built in reader. But that power drain is beyond what I can accept.
I haven't tweaked anything, so if there's something I might have missed or not done that would decrease the drain let me know.
Wifi was off, light was around 5, natural light was off.