does anyone know what to do?
Halon is for electrical fires and it will kill you if you breath it. Most hardware stores sell fire extinguishers that are specialized for home or for automotive use. Also, if you are concerned about electrical fires the best bet is to get a battery cut-off switch.
Come on do your own physics homework. Its more fun that way when it doesnt crush
A 1-5 lb. ABC dry chemical extinguisher should suffice for your car. They can be easily mounted in the trunk, out of the way. This also puts it as far away from the engine which is where you're most likely to have a fire. KIDD is a good, reliable, and inexpensive brand and is sold in most hardware and automotive stores. By the way, Halon is used for computer and electronic fires and is not available to the public, and is no longer manufactured due to its ability to deplete the ozone. Also a battery switch will do nothing to stop a fire once it starts.