I updated my Apple Watch 4 to the latest OS 7 and where my battery was 60% charged when I went to bed I am now getting red low battery warning by 9 p.m. Looking at Apple Communities, I am very much not alone, so be warned.
My sympathies. As a night owl I find going to bed very draining. Have you tried reducing one or two of those exciting, but maybe non-essential, new apps?
This lists a bunch of symptoms that you might experience after updating to watchOS 7, including ‘increased battery drain on your iPhone or Apple Watch’, and includes what sounds a very tedious solution.
This article has a theory about why re-pairing the watch might help. I notice that he apparently managed to fix it without going as far as wiping and restoring the phone as well.
On a bigger sample of days, I think my battery usage (Series 5) has not changed.
Note that my suggestion about hand washing was intended to be humorous (though I do find myself making sure the 20s timer completes so I guess that counts as a success).
David Moon 