Hi.
My two cents on battery drain. I'm now on watchos 11 RC & apple watch 9. Exactly how I had for wathcos 10, the main reason for battery drain (up to 7-10 % per hour) is the watch face! In particular even if it's absolutely my favorite, stay away from "analog solar" one. On watchos 11 the new "reflex" one seems to have the same draining behavior.
Very weird is that not using is not enough: you must also remove from the face gallery and reboot the watch.
Once done my watch instantaneously reverts back to expected battery duration (less then 2% / hour ).
I hope it may help someone.