Bought a Galaxy Watch 3 in January, battery has slowly but surely getting worse.
This morning I took it off the charger at about 09:00 and battery life is 62%. So in 3 hours its reduced by 1/3.
Black face watch with black background. Brightness is 1 with auto screen on off. Wifi off, NFC off, Location off, HR reading every 10 mins, Optimize battery ran every day. I use it to look at whatsapp notifications basically but this is unuseable