This is your battery or charging light. What should you do if it comes on while you're driving? If your battery charging light comes on while you're driving, you should pull over as soon as it's safe. This light comes on when your alternator is not making electricity and the car is running off of battery power alone. 1  You can drive a short distance on the battery, especially if you turn off most of your car's electrical items (like the radio, air conditioning, etc.), but there's no way to know how far you'll get before it dies.