If you are having problems with Google Play Services eating up your battery, it was showing 60% on my Watch 6 classic. The fix I found to work was on your watch go to Play Store,, scroll all the way down to manage apps, tap on Google Assistant, tap on uninstall, then tap on update, Google Assistant. This will give you a clean update.
It now no longer eats my battery, the below screenshot in the Wearable app is typically how it should appear of normal usage!
You can also wipe cache partition on your watch as you do on your phone, below is a video on how to do this, it will help if your watch is getting laggy.
This post was edited because my verbiage was not totally accurate as the responses show.
