The computer has detected a fault with the battery and charging system.
On a modern car it will need to be scanned to see why the computer is angry.
On an old (older than mid 90's) car you have to figure out whats wrong with the alternator.
Have the charging system checked. The light comes on when there is a charging system problem. it may be a battery, alternator or a battery problem.
the battery light means that your battery is being charged properly. so let it light.
If your engine is running , and the battery light comes on , that indicates that your battery is not being charged
Disconnect the negative battery cable for about a minute Disconnect the negative battery cable for a minute or so
Your battery is not being charged
Defective alternator or bad wiring.
The battery light comes on when the alternator output voltage is too low or too high. You have a wiring or regulator problem.The battery light comes on when the alternator output voltage is too low or too high. You have a wiring or regulator problem.
disconnect your negative battery terminal for about 10 minute then reconnect it. If it comes back on you my need a repair shop to reset it or check to see what is making the light come on
Remove battery cable for one minute .
The battery light usually comes on if there is a charging system problem Either battery or alternator are the usual causes.
Faulty Alternator?
If the battery light comes on when you try to start your car, either your battery is low or your alternator is going bad. These can be checked by going to an Advance Auto or Auto Zone, they will test it for you for free.