I replaced my own battery. After a couple days, I'm coming home from work (12hrs) with over 50% battery life. Just make sure you buy a separate kit to open the watch as the screwdrivers that come with the batteries suck.
I replaced mine as well just the other day with the replacement from iFixIt. The battery life is indeed better but I am still only getting about 8-10hr of battery life out of it. This occurred after an update from Samsung to their new Tizen version. The battery use indicator says that the watch settings app is using used though I have closed all apps and haven't touched the thing all day.