My Dell XPS15 L521x seems to have some screen problems. When plugged in the brightness is fine and brightness control works. When I unplug the ac adapter and the laptop is running on battery, the screen becomes very dim, and flickers at times. Changing brightness doesn't seem to do anything, only making small differences on brightness from minimum to maximum. The brightness is just as dim when in bios before windows. Here's a quick video of the problem. start up.