I started to notice that my S7 used a lot more battery than usual some days ago (battery went down from about 95% to 50 % when I was asleep). And at the same time the phone got hot during charging. Before this occured I didn't do anything in the settings and have always used the original Samsung charger.
So I went through the battery and app settings and saw that the Always on display was the top user with 16 % since the last charging. It didn't sound like anything remarkable, but I turned off the Always on display. I went through the app list, and no app did really use any battery at all.
I also did restart the phone after that (which I haven't done in a while).
Well, as it turned out, the phone in now cold while charging, and doesn't use near as much battery while not used. I really don't know what solved it, but it's okay now.
I'm not an expert, but maybe this could be helpful for someone with the same issues.