I’m seeing similar on my watch 7, but have been seeing the approx 20% drop since night 1 of beta 1 on a 22:30 to 06:15 sleep schedule. watchOS 9 used to drop 10 to 12%, starting from a full charge before going to bed.I'm currently losing about 20-25% over night during sleep (roughly 00:00-09:00), same for B2 & B3. First couple of nights was only 10-12%
Battery consumption on betas is always terrible with unoptimised code and a ton of extra diagnostics logging going on behind the scenes - I’ll start to worry about it if it is still using 20% on the final release.