How to Jump a Car Battery

How to Jump a Car Battery

The headlights and interior lights of some cars turn off automatically when the key is removed. In other cars, the lights stay on indefinitely. Combine these mechanical tendencies with the forgetfulness of the human mind, and this means that at some time in your driving life, you'll go to start the car and find that it turns over hesitantly once, and then refuses to do anything but click at you. The battery is dead. Luckily, cars are equipped with an alternator that—as long as it's functioning properly—will recharge your battery once the car is started. Of course, to get it started, you need a power source. That's where jumper cables come in. Nothing brings people together like the need for a jump. Flag down a fellow human or recruit a neighbor, and then follow these steps to ensure that you both emerge from the experience safe and unjolted.

TOOLS:

• Jumper cables

• Wire brush

1 Move the cars into position. Look under the hoods to see where the battery is located in each car. Drive the car with a live battery alongside or in front of the car with the dead battery so that the batteries are close together, or at least close enough so that jumper cables will reach from one to the other.

How to Jump a Car Battery

2 Connect the two batteries together. It's not difficult to properly connect jumper cables between the live and the dead battery, but it's extremely important to do it right. First, turn both cars off. Locate the positive and negative battery terminals, which should be labeled with + and –. The positive terminal may also be covered by a red cap. Start with the live battery—if the battery terminals are corroded, use a wire brush to scrub free any rust. Then connect the red, positive strand of the jumper cables to the red, positive terminal on the good battery. Move to the dead battery and do the same thing, attaching only the positive jumper cable clip. Then attach the negative, black, clip to the negative terminal on the good battery. It used to be that batteries couldn't help but leak a small amount of flammable acid. It's not such a good idea to have sparks around flammable acid, so in the old days people clipped the negative side of jumper cables to the car's metal frame to ground the current. New batteries almost never leak acid and so this configuration is less important. To be safe, if your battery is more than 15 years old, clip the negative end of the jumper cable to an unpainted section of your car's metal frame (likely underneath); otherwise, clip it to the negative terminal on the dead battery.

How to Jump a Car Battery

3 Start the car with the good battery and leave it running. As soon as you connect the jumper cables, the good battery will start charging the bad one. If the dead battery is really, really dead—that is, turning the key still does absolutely nothing—you may need to let the good battery in the running car feed some charge into the dead battery for a while before trying to start the dead car. Keep trying until it starts.

How to Jump a Car Battery

4 With the cars running, disconnect the cables. Though it doesn't matter in what order you disconnect the cables, be sure to keep cable clips from touching each other until you've pulled the clips off at least one of each battery's terminals. If the cables remain connected to both terminals of either battery, and then you touch the other cable ends together, you'll complete a circuit and create some rather exciting fireworks. Don't make fireworks.

How to Jump a Car Battery

5 Leave the dead car running. Assuming a depleted battery was the only problem, with the car running, the car's alternator will recharge the battery and no additional action will be required.

When You Need More than a Jump

Diagnosing your battery. After four years your car battery will start its slow fade toward the recycle bin. It might make it a few more years, but be on the lookout for signs of age and nip a fading battery in the bud before it strands you in a downpour. Unfortunately, battery testers offer imperfect diagnoses, as they are unable to tell you how long that battery is likely to hold a charge. So get under the hood and check the battery yourself. Remove the case and look for corrosion or leaks. Clean buildup around the terminals with a solution of baking soda and water. Keep in mind that long periods of inactivity, high gadget usage, and living in an extreme climate will all shorten battery life. And if it's been more than four years, err on the side of caution: When in doubt, replace it.

How to Jump a Car Battery

Signs of a bad starter. If you have a battery tester, use it to test the battery. Without a battery tester, it's hard to disentangle a dead starter from a dead battery. But if you've properly connected a dead battery to a live one with jumper cables and the car still refuses to start, it's a good bet the starter is to blame. In that case, call up the tow truck.

How to Jump a Car Battery

It could be the alternator. Do you notice the lights on electrical components getting dimmer while you're driving? Maybe the gauges are flickering. A warning light in your car should signal ALT or GEN when your alternator's gone south, but you can't always count on it. Instead, it might take a dead battery followed by inability to recharge to diagnose a dead alternator. That said, when you first notice your battery failing to hold a charge, check the belt running from the alternator to the starter. If it's loose, tighten it by using a socket wrench to loosen the alternator. Push the alternator back until it tightens the belt, and then retighten the alternator bolts to hold it in place. Also check the electrical connections into and out of the alternator to ensure that there are no loose or frayed wires. If everything looks good, then the alternator itself is bad.

How to Jump a Car Battery

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