I am writing this section at the request of one of my readers who wondered why there was nowhere on the web that she could read about jump-starting a car with a dead battery. As with any procedure involving opening the hood of a car there are several precautions you should take to avoid injury - I mention them as we go along so read the article completely. If you are unsure or feel as if the procedure is too dangerous or complicated, by all means get someone who is knowledgable to help you so as to prevent injury to yourself and damage to your car. I assume no responsibility for damage or injury you cause while following these procedures! So here is the safe and simple way to do it:
Before we get started you should understand that there are many reasons for a battery to go dead. If you know that you have left your lights on and you are reasonably sure that your battery and charging system are in pretty good shape you can just jump-start your car and be pretty sure that it will recover from the temporary problem you have encountered. If, on the other hand you know that your battery is pretty old (three or four years, typically) and/or you have experienced multiple dead batteries with no obvious reason, you need to perform some diagnostics to find the problem. This article deals with the simple and safe steps to get you started and on your way.
You will need a few essentials before attempting this task. First, you will need a good set of jumper cables. Good cables have multiple stranded copper wire, about four gauge. It usually says it on the box. The "alligator clips" should be copper as well and the junction of the wire and the clips should be secure. Soldered connections are best but a really good crimp will suffice. When you buy jumper cables go for the extra buck and get them longer than your car so that you could possibly get a jump-start from someone parked behind you.
You will also need a willing participant to offer their car (and battery) from which you can jump-start your car. It helps if you open your hood and stand there with the jumpers in your hand with a sad, forlorn look on your face. It doesn't matter if the "volunteer's" car is smaller than yours. I have jumped my own car using a John Deere garden tractor.
Third, and don't take tis lightly, you need some form of protection for your eyes. Safety glasses with side shields would be perfect but the chances of you having them readily available are next to nil. I think that all jumper cables should come with safety glasses as a requirement, but that's just my personal opinion. Use sun glasses or your normal reading glasses or whatever you have available - you will see why as we continue.
Once you have made arrangements with a volunteer get the cars as close as necessary to comfortably connect them together with the cables. Open both hoods and locate the batteries. If it is dark get a flashlight so that you can make a definite identification of the battery terminals. The identification of the polarity of the terminals is critical - don't guess else you can do SERIOUS damage to yourself and/or the car's electrical system. Batteries all have one characteristic in common. They all have one positive and one negative terminal. This is where the car's internal cables connect to the battery. On older cars you may find that the terminals are on top of the battery, however most newer cars have their terminals on the side of the battery, making them nearly impossible to see, much more difficult to clamp an alligator clip in place.
OK, so you have the hoods open and good lighting available. What now. Look for one or both of the following identification marks near each of the terminals; find either a plus (+) sign or a minus (-) sign. Or, look for a red or black marking on the battery cables or terminations. Red is positive and black is negative. This is a universally common standard in the automotive industry.
A note here about one of the dangers concerning what you are about to do. Batteries are charged by the alternator on your engine. When they are charged they internally generate both hydrogen and oxygen gas from the electrolysis of the water - remember your high school chemistry class, H2O? Well, if you make a spark in the vicinity of the battery there is a pretty good chance that you will ignite this highly combustible mixture with a resulting explosion and very rapid distribution of battery acid!!! Bad Stuff!! Also be aware that even if you do connect the batteries together correctly there is a slight chance that one of the batteries could explode due to an internal short circuit in either battery. Never place your head directly over the batteries during these procedures!!
So, what's next? We've need to connect the good and bad batteries together - positive to positive and negative to negative terminals. But there is a hitch. You see when batteries are charged they generate both hydrogen and oxygen gasses internally. The combination is highly explosive, so we don't want to risk touching off an explosion by making sparks in the vicinity of the batteries. The secret is to make the connection between the cars somewhere else besides the batteries.
Virtually every car made today has its negative terminal connected to the engine. The positive battery cable is connected to a terminal on the starter solenoid. So, when we connect the batteries we first connect the red jumper cable to the positive terminal of both batteries. Be extremely careful that you don't accidently connect the positive cable to the battery and then let the alligator clip hit some nearby metal - it will make a large spark and may cause an explosion. Then we connect the black jumper cable to the negative terminal on the good battery. Next, find a heavy bracket or other metal part of the engine block on the other car and connect the black cable to it. This will probably cause a spark but if there is a spark it isn't close to the battery so there is no danger of an explosion.
With the batteries connected we now start the good car's engine. Make sure that the jumper cables are not interfering with the fan belts or the serpentine belts and pulleys - dress them neatly over the fender of both cars and be careful of not tripping over them especially in the dark. I usually leave the batteries connected with the engine running for a few minutes to charge the dead battery. Now start the car with the dead battery. If it doesn't start right away make certain that the jumper cable connections are tight and that the jumper's alligator clips are on clean, rust free surfaces. Wiggle the clips and try it again. Long jumper cables, especially the cheaper ones, can't carry the 300 amps or more required to jump-start a car so letting the good engine run at a fast idle for five or more minutes will charge the dead battery and take some of the load from the jumper cables when you try to start the car with the dead battery.
Once the car has started run it at fast idle for a few minutes. Assuming that its charging system is up to snuff, this will charge the battery sufficiently to restart the car after the next step. To make sure that you aren't injured I recommend that you now turn off both engines so that you can safely remove the cables without getting tangled in the moving parts like fan blades and belts. Remove the cables in the reverse order that you used to hook them up, taking the ground cable clamp from the engine metal first. After removing the cables immediately re-start the car. If you feel comfortable removing the cables with the engine running have a care about loose clothing and fingers and keep the cables away from moving parts.
Next step is to close the hoods, profusely thank the volunteer who helped you and go home.
If the battery had been run down completely or if the weather is below freezing it is a good idea to charge the battery overnight. If you don't have a battery charger you can purchase one at an auto supply store for around twenty five bucks. Connect it using the color codes discussed previously. Most chargers can be left connected indefinitely since they are voltage regulated and won't overcharge your battery.
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