I have the samsung galaxy watch 3, had it for about 6 weeks now and used to get almost 2 days before needing to be charged, lately I'm getting a day at most, I've not installed anything new, not doing anything different tracking wise, took it off charge an hour ago said 1day 8hrs of charge, just looked and already gone down by 13%! Now says 1day 4hrs left, but I know it'll need to be charged again before bed, why is my battery draining so quickly?
Sounds like you have a rogue app using up background data. Have you recently added a 3rd-party app on your phone to track your health, etc? It is also possible that your watch is trying to interact with your phone more than normal.
Perform a hard-reset of the watch, and see if that helps.
my watch has been so much better since it went in for repair, they replaced 3 things inside so more than the battery, I get 2 days now per charge, I would contact customer support and see if they can collect it for inspection and possible repair.