Then you have way too many apps running in the background. That is a typical Android problem. You exit the app, but it is still running in the background.
Download this from the App Store, "Battery Doctor".
Problems are over...
very configurable to accomplish just about anything you need in the way of power management.
https://play.google.com/store/apps/details?id=com.ijinshan.kbatterydoctor_en
The included Widget is very nice. I just tap that thing and all of the background stuff is terminated. IF the screen just goes away, or I hit the power button to quickly turn the phone off, the Widget will after a few moments note you are not using the phone... then it cleans house....
This app will apps hours to your battery life...
It also monitors the charging rates, and slows the charge down to a trickle charge for the last 10% approx ~ to prevent overheating the battery.
Worked a treat on my original Galaxy S Fascinate.... and just as good on my S5.