Same problem with Watch 3. I had to charge it 2 times during the day yesterday, and it completely drained overnight.
Battery usage showed ~20% watch face, ~20% samsung health so I applied minimal watch face but no obvious difference on battery life.
Did a backup, reset, restore , I'll let you know if this fixed the issue.
That doesn't seem right to me @Bexstar . Would you be able to let the watch battery drop under 50% from a full charge and send us a screenshot of the battery usage so I can see if there is anything malfunctioning or draining too much battery?
You can get this info from the Samsung Galaxy Wearable app > Settings > About Watch > Battery.