I think that most of us know that the term “Jumper Cables” means the pair of heavy wires with black and red clamps on the ends that are used to connect a car with a good battery to one with a dead battery in order to get the latter car started. Actually, every car should carry a set of jumper cables, even if the owner has no idea how to use them. If you get stuck with a dead battery in a parking lot, there is often a good Samaritan around who will help you use them to get your car started. Sooner or later every battery goes bad, or gets discharged because you left some lights on. Fortunately, this is more likely to happen in your own garage than in a parking lot because a battery that is going bad discharges one of its cells all by itself, and that usually takes a few hours. For this case you should really also keep a battery charger at home, but jumper cables will suffice here as well with the help of another car. BTW, if your car has a spare tire mounted inside the vehicle, wrapping jumper cables in with that is a good place to store them. And it’s better if you know how to use them safely yourself, so here’s how:
To charge a dead battery with jumper cables, the engine of the working car must be left running so that its generator is producing electricity, and all lights and other electrical devices should be turned off in the car with the dead battery.
Car batteries have a positive and a negative terminal in which the positive one usually has a red plastic cap covering it, and the negative one is connected to the frame, and hence all of the metal of the car. Whether or not the positive terminal has a red cap, the positive terminal is marked with a “+” (plus) sign, and the negative one with a “–” (minus) sign. The red-capped (positive one) is called the “hot” terminal because, if any electrical conductor (wire or other piece of metal) were to touch both the hot terminal and any metal on the car, then sparks would fly and the metal would get extremely hot in a big hurry. Car batteries are capable of furnishing a very high electric current.
In addition, hydrogen gas (which is very flammable) is produced when a car battery is either being charged or discharged, and more so when the charging/discharging current is high as in “jumping“ a dead battery from a good one. Since this hydrogen could be ignited and explode if a spark were to occur near a battery, a particular sequence of connecting up the jumper cables in a safe manner is necessary. Proceed as follows:
Remember that, at all times, you must see that the two clamp connectors at each end of the cables DO NOT touch each other. If that happens when the other ends are connected to a charged battery, you produce a “short circuit” and sparks will fly. One way to assure safety is to connect one of the clamps on to the insulated portion of the cable while you connect up the other ends to the dead battery.
First, lift off any red plastic cap and connect a red jumper clamp on to this positive terminal of the DEAD battery. Then connect the black clamp to any heavy metal portion of the car away from the battery. Connect the clamps on solidly, scraping through any dirt if necessary to make a good electrical connection, and assure that the clamps won’t slip off. Next connect the opposite red cable clamp to the hot (positive) terminal of the good battery. Lastly, connect the black clamp to any heavy metal part of the car that is away from the battery. When finished, the two “hot” terminals should be connected together by the wire with red clamps, and the metal of the two cars should be connected via the wire with black clamps. You should see some small sparks when this final connection is made. That is a good indication that you now have a complete and working connection, and electrical current is flowing.
Do not immediately try to start the stalled car. Wait several minutes for the current flow to get some significant charge into the dead battery. If the weather is very cold, just sit in the warm car and let the other battery charge for five minutes or more. Cold or very dead batteries do not accept charge at a high rate, and furthermore you must put more charge into the dead battery to start a very cold engine.
After starting the disabled car, remove the cables in the reverse order of connecting them, again making sure that the black and red clamps at NEITHER END of the cable touch each other until completely disconnected. Unless you know why the battery is dead (e.g. left on your headlights), you need to get your car to a service station or garage to get the electrical charging system and the battery checked out.