I charged my watch to 100% around mid day yesterday and today at mid day before my 50 minutes run it was already at 93%. After my run it was at 91% and now it's at 89%. So it looks like indeed about 10% per day when it should be 5%. I am ok with the 2% usage during the run but not with the watch using 9% while barely using it.
I am on 12.35 using stock watchface I have auto back light off, gesture mode off, brightness 10% with 4 seconds back light. On demand pulse OX, GPS auto and Bluetooth and Wifi on.