Hello yesterday i bought DELL Inspiron 15 (3542) win 8.1. And noticed that if charger is plugged on, screen becomes brighter, and after unplugging dimmer. Of course i tried adjust screen brightness, I've tried changing all power plan settings, changed advanced power settings to max. tryed go to bios but there was nothing about brightness. i tried use brightness buttons on keyboard no matter if charger is plugged in or not the bright bar is still set to full, however the bright difference still exist. the bright difference then charger is on are about 4%-6% . then i pull out the charger the screen becomes darken in few sec. and i noticed that after closing and opening the led(then computer is using only battery power) at the start screen is same bright as with charger plugged in. My sister have older Dell laptop(bought 4years ago) and for her the bright difference was about 50% but i repaired that through Bios. So how i can fix that uncomfortable issue?