I have the Galaxy Watch Active. I purchase from Samsung on April 2020. Battery last for 2 days. Since Tuesday 05/5/2020, battery last for 5 hours. I have to charge it 3 times daily. My current software version is R500XXU1DSL1/R500OXA1DSL1.
I've also had this problem. The past 3-4 days my watch won't last even 6 hours without dying. i have tried every single "fix" I've found on the internet, including resetting it, and its still dying. I've had it off the charger for 3 hours and it's at 39% battery life. My expensive watch is now unusable.