Same with a Watch Series 7 WiFi only. Watch losts nearly 20% battery overnight and also with my iPhone 12 with latest iOS 16.6 which sees his battery drained.
I lost nearly 50% over 6 hours just wearing them in pocket !
Watch becomes a little hot while iPhone is warmer and hotter than previous days.
They are doing nothing: no always-on display, WiFi and Bluetooth activated and I wear the Watch on my body, iPhone is on the desktop.
Switching OFF notifications, do nothing in 6 hours : 50% battery drain on iPhone 12 and 45% on Watch.
This is impossible.
Weather is 24°C on my location.