The greatest drain is almost always the screen, as powering the backlight for your tablet's large display uses a lot of energy. Step 2: Turn the screen brightness level down. Adjusting the brightness level of your tablet’s screen can save a lot of battery power. To do this, open Settings – Display - Brightness. A pop-up window will display a slider which you can use to change the brightness level. If the slider isn’t visible untick the box marked Automatic Brightness.