A jumper cable is a set of two thick, heavy duty wires with alligator clips, otherwise known as jumper cable gauges, at both ends. They are used to jump start, or give a quick boost of energy to, vehicles that have dead or drained batteries. By jump starting a car, you use a second battery, usually from another car, to give your car’s dead battery just enough power to get the engine started, which can start the alternator working. The alternator is an electrical generator attached to the engine that uses the engine’s rotation to generate voltage, which is then used to recharge the battery. Jumper cables come in sets of two, a black one for the negative side and a red one for the positive side. The two cables are identical and therefore interchangeable, but it is very harmful for car batteries to connect the positive side of one battery to the negative side of the other, so it is important to use the black only for negative and the red only for positive as a precaution against human error.
Because thicker, heavier jumper cables will conduct more energy, they are superior to smaller cables. There are small cables available at gas stations and department stores that you can buy for around $20, but these are not recommended. Especially if you drive a big truck or SUV, you should buy the thickest cables you can, just to make sure that they are capable of conducting enough energy to jump start your car. Big jumper cables are also better because they have bigger alligator clips, which means that they can form a more solid connection between the two terminals of the two batteries.
If your car doesn’t already have a voltmeter built in to the dash gauges, it is a good idea to buy a small hand held voltmeter to carry around with your jumper cables. This can help to make sure that your jumper cables are connected correctly between the two batteries. If the car won’t jump start, you can make sure that the jumper cables are making a good connection to the battery terminals by touching one lead of the voltmeter to each of the dead battery’s terminals while the two batteries are connected. If there is less than 12 volts across the terminals, either the cables are not making a good enough connection or the cables aren’t thick enough to get the necessary amount of power across.
The only difference between different kinds of jumper cables is their thickness, and the thicker the cable, the more energy it can transmit from car to car, so it is generally considered best to buy the thickest cables you can afford. It can be extremely frustrating to have the battery in your car go dead, but even more frustrating to be stuck in the middle of nowhere with no way of reviving your battery, so you should make sure to always keep a pair of jumper cables in your trunk.