It's Possible that your Apple Watch is starting to see the end of the battery life depending on when you purchased it.
Here's what I suggest:
1.) To determine the overall battery health of the Apple Watch, Apple can conduct a free battery test of the Apple Watch over the phone or in store. 80% is there grade line.
2.) As for your concerns with your battery having drain issues, try the following:
- conduct a hard reset by holding down the digital crown and power button for approximately 10 seconds until you see the Apple logo.
-Once the Watch reaches the home screen, Then fully drain the battery to zero and then recharge it back to 100% percent.
Also, keep in mind if you're running a beta, that could be part of the problem. And third-party applications are a massive culprit that affect the performance of the battery with the first generation Apple Watch at times.