The most common reason for the battery light to come on is because the voltage of the battery is too low. This could be caused by a bad alternator or a dying battery. If you are able to jump-start the car and the light goes off, then it's likely just the battery that is the problem.
Alternator Problems
If the alternator is not working properly, it won't be able to generate enough power to charge the battery. This will cause the battery light to come on and will also eventually kill the battery. Replacing the alternator is usually necessary if the alternator is the problem.
Loose Connections
Sometimes the battery light can be caused by a loose connection between the battery and the alternator or the ground. Make sure all connections are tight and that no corrosion is present.
