If you leave your light s on a car twice and the battery is dead will this make weak?

No , this will not make your car weak . This is because when the battery is dead , there is no power flowing through the car's electrical system , so the alternator will not be working to generate electricity . As a result , the car's electrical components , including the lights , will not be drawing any power from the battery . Therefore , leaving your lights on with a dead battery will not weaken your car .