As many people on this forum, I have a galaxy active 2 that overheats and drains the batter when charging. I have a solution that actually works! I have automated plugs in my house so I plugged the watch charger into one of these plugs. I then cycled the plug, 1 hour on and 5 hours off. The watch keeps a full charge and I have not received the overheat method since doing this. If you do not have automated plugs, I suspect even a mechanical timer timer would work. I also suspect you could tweak the cycle time to keep the watch even cooler.
I know it is a bit of a kludge, but until samsung does something this is my work around.