Hi,
Thank you for using the Apple Support Communities! It's my understanding that you are experiencing shorter battery life since updating to watchOS 6. I am happy to help.
Depending on when you upgraded to watchOS 6, there may be a new update available to complete. Please complete any available updates for your Apple Watch Update your Apple Watch - Apple Support, as well as the companion iPhone Update your iPhone, iPad, or iPod touch - Apple Support.
Once updated, we ask that you use your devices as normal for at least 48 hours after updating. During the first 48 hours after an update, it is normal to see unexpected, quicker battery drain, as the new software settles in by completing general digital housekeeping required for new OS. We also ask that you follow any tips or suggestions for maximizing battery life as discussed here: Batteries - Maximizing Performance - Apple.
If you continue to experience unexpected battery drain after following those tips, and waiting 48 hours after updating, I would like you to reach out for continued support using this link instead, please: Contact - Official Apple Support.
Thank you for your time!