Having the same issue and just replaced the battery - brand new battery lasts 4-5 hours with normal usage. Posted details about it on another similar thread here so won't repeat again, but clearly there's a problem that Samsung is not acknowledging.
Samsung, why are you being so quiet?, I spent alot of money taking a leap of faith leaving Motorola for the S3F and Note 8. Maybe this is not the company to be brand loyal.
On June 8th I received a sizeable update to the Wear app and the watch. I have gone from 8 hours of battery life to 32 hours, with all my apps loaded on the watch. Looks like Samsung has begun rolling out a solution to the battery drain issue. Thank you Samsung.
I have the same issue and have gone through all the solutions found on the web, reset and recovery options for several times, deactivating nearly everything such as AOD, GPS, wifi, Samsung health, diagnostics report, using grayscale display, low brightness. I put the watch on airplane mode and the battery drained to 50% within 6 hours!!
Dear Samsung, I have been loyal to you during the last decade! But this awful experience for which you keep silence and inactive makes all of us disappointed. It depends on whether you want to keep these customers or not. For me, I have already started looking for other options because even cheap no-name options on the market have a better battery life than my Gear S3, six-month-old watch.