Doze

Doze is an app to improve your Android battery performance. The way it does this is as simple as it is effective: by blocking certain apps from using data while the screen of the device is off.

When you turn your screen off, the apps running in the background actually keep using data, either via WiFi or 3G/4G, which consumes battery – eventually a lot of it. What Doze does is basically stop certain apps from consuming battery this way. Obviously, you would want some apps to keep working so you receive some notifications, such as WhatsApp or Gmail, but you might not be very interested in others, and those are the ones you could block.

In the settings you can customize a few options, such as stopping Doze whenever you are connected to a WiFi network, or whenever you plug in your device to charge it.

Doze is an especially useful app for those who have Android versions prior to Lollipop, since those don't include any option to save battery, unlike Android 5.0 and 6.0. But whichever Android version you have, this is an excellent app with some very useful features.