Battery usage for keeping apps open
In Linux/Android it is not recommended to close apps or use task killers.  Unlike a Windows computer/phone, Linux/Android can keep applications &quot;running&quot; in the background which doesn't use any CPU or networking (unless it's a media player).  It has actually been proven that closing apps causes more battery drain, because instead of Android being able to recall the app that was in memory it has to relaunch it, which requires more memory use as well as CPU.
You are better to leave apps running.
Sources:
How To Geek and
LifeHacker