The screen, not surprisingly, is a tablet's biggest energy hog, as this screenshot from GSam Battery Monitor, a power usage analyzer for Android, shows. It's unwise to set your tablet to maximum brightness, as battery life will suffer greatly. The iPad's auto-brightness setting adjusts screen brightness based on ambient light, and Apple says the best way to extend battery life is to manually adjust this setting. To do so, go to Settings > Brightness & Wallpaper and drag the slider to the left. Android users should go Settings > Display > Brightness. Unfortunately, reducing screen brightness might result in a less enjoyable reading experience, but battery misers must learn to live with trade-offs.