I have been dealing with this exact problem since the s3. I've tried everything everyone is suggesting on here and in YouTube. I've rooted my phone, run all the battery stats apps, used the battery saving apps like Greenify, pretty much you name it, I've tried it.
This last go-round, I ended up with an s7. I decided against rooting this one because the methods were iffy at best and were error-prone anyway. So Greenify didn't do any good when I noticed the phone getting hot in my pocket.
I installed BetterBatteryStats and granted it "root" privileges using Android Development tools. This method identified a couple of problem apps (Facebook, Messenger, etc) so I installed those.
Things got better for a little bit and my phone wasn't getting hot as often, but then the battery started dying early again after a few weeks. That's when I discovered Samsungs in-house battery and app management software.
Though I couldn't pinpoint an exact application using up the battery but background data or CPU usage, I knew it had to be one of those causing the phone to heat up. Using the Samsung software, I disabled background data usage for every app I deemed to be non-essential, which basically meant everything that wasn't SMS, launcher or system. Then I went through the battery settings to toggle always sleeping mode on these same apps. After doing that, I was back to 20-30% at the end of the day.
Every once in a while I have to check these two settings to set any apps I may have installed to the correct settings. Also, I have recently found an app called AccuBattery that monitors app usage and recommends when to disconnect the charger at around 80% to prevent excess cycling on the battery. As an aside, this app also analyzes battery health and shows that my battery has about 66% of it's stock capacity due to my bad habit of charging overnight every night. Shame on me. But at least I know what to do next time around!
Hope this helps someone. It's a lot of work, but it's worth it. And what's great is that I don't notice any difference between in terms of notifications and keeping in the loop but I have a faster performing device that lasts all day without heavy usage.
