My iPhone was going dead so I plugged it in the car charger and it charged up to about 5% and then stopped charging and went dead. I then tried using 3 different chargers and plugging it into the computer but it will not get any power. I can hold down the buttons and get the screen telling me that it is dead and I need to plug it into a charger but it is plugged into the charger! What could be wrong? Thanks in advance!