Android now optimizes apps so they won’t drain the battery as much. For example, your email app can still run in the background, checking for updates, but it does so less frequently. However, you can exempt certain apps if you want them to always run at full throttle. Open Settings and tap Battery, then the menu button on the top right, then Battery Usage. Here, you’ll be able to see which apps drain your battery according to how much you use them. Tap on any of them and then on Battery Optimization. Next, hit the Not optimized link, then All apps. Finally, select an app and pick the Don’t optimize option.