I am having this issue too, it literally takes 8-9 % every hour! It only drains the battery when the watch is connected to the phone.
The same happened after the last update 6.2.5. , I waited for several days as advised, didn’t helped, I've restarted both the phone and the watch.. didn’t help, Unpaired the watch... didn’t help, reset the phone‘s network settings and paired the watch again... didn’t help either and then I played with the airplane mode and switching off the Bluetooth, and that worked, so after about a week after the update my watch was back to normal 2 days of battery life.
Then 6.2.6 Update came. At first I was reluctant to update and when my partner updated and after a day or so his watch battery life was back to normal, I decided to update mine too. Big mistake!
it’s nearly a week and I need to charge my watch twice a day.
I would appreciate any advice.