If you sometimes experience Android phone warming up, overheating, or battery draining, quickly check apps consuming battery, and stop them !
It may happen that some apps keep using battery in background, even though you are not actually using them.
First, open settings. Find the Battery menu. Look for the apps with a high percentage (see below examples with 9GAG, Facebook or ZenUI Launcher). Select the apps one by one, and click on Force stop.
Should you not use the app at all, don’t hesitate to go in the App info, and uninstall it.
The applications Android System, Android OS, and Screen, should normally be the ones using the most battery, as they are vital to all phone usages.