Board Thread:Questions and Answers/@comment-27331024-20150930202852/@comment-26927141-20151005135905

I know for iOS 9 and up, if you put your phone in battery saving mode, it automatically suspends the game when you're not in it so it's not dragging power. And otherwise all you need to do is go to switch windows, and swipe up on the program to stop it from running while you're not in it.