I have the Apple Watch 7 with 10.1.1 and terrible battery drain. Updated to 10.2 Beta but that update still didn’t fix it. Battery would go from 100% to 20% after 7 hours of wearing it and not actively doing anything on it.

I went through “background app usage” and turned everything off with only the normal apps/services I actively use and my battery is back to normal. It’ll drain down to 40% after 12 hours. Maybe IOS has some weird background app drain issue. Worked for me, easy to try and rule out as a fix if you are experiencing these issues.