Since the system is under a  year old, it's under warranty.  Call Dell -- either the battery is faulty, or the system board is, but the warranty will cover the repair.  
MY LAPTOP IS DELL G15 5520 I HAVE BEEN FACING THIS ISSUES AFTER I'VE REBOOTED MY LAPTOP. I CAN'T START MY LAPTOP(EVENTHOUGH THE KEYBOARD WILL HAVE LIGHT FOR A 3 SEC BUT IT STILL WON' START UP AND I THING IT IS NOT THE BATTERY PROBLEM) WITHOUT AC ADAPTER AFTER I STARTED IT, IT CAN BE FUNCTIONING WELL, BUT IT WILL IMMEDIATELY SHUTDOWN AFTER I TAKE OFF  THE AC ADAPTER.  
CAN'T START LAPTOP WITHOUT AC ADAPTER