How to jump-start a car

A dead car battery can leave you stranded and be a real headache. But if you carry jumper cables or a battery jump box in your trunk and know how to use them properly, you can get back on the road in a few minutes. 

Edmunds goes more into detail below, but if you need a quick solution, here is how to jump-start a car. If you're using jumper cables, connect the red clamp to the positive (+) post on the dead battery. There's often a red plastic cover near it. Connect the red clamp on the other end of the cable to the positive post on the working battery. Next, connect the black clamp to the negative post (-) on the working battery. Finally, you'll want to attach the last black clamp to an unpainted metal surface under the hood of the car with the dead battery, then start up both cars with the donor car going first.

If you're using a jump-starter battery pack, make sure the cords are connected to the box, then connect the red clamp on the positive (+) post and the black clamp to the negative (-) post. Make sure the jumper box is turned on. Some will have a green confirmation light to indicate that the connection is good. Start the car and it should do the trick. If not, try again and if that fails, your battery is likely completely drained.

Once your engine is running — and if the battery is still good — the alternator will recharge the battery. If the car battery dies again or the jump start does nothing, call roadside assistance or buy a replacement battery. Often, stores will install a car battery for free, but call ahead to make an appointment if possible.

Take precautions

Jump-starting a car is relatively easy, but you should do it with caution. Since the car battery is often located in the engine compartment, where flammable gases may be present, a spark could set off a fire. The goal is to hook up the weak battery to the live battery in the booster car without creating any sparks. Connecting the jumper cables in the right order will minimize the chance of sparking.

It's important to make sure the metal ends of the jumper cables do not touch each other or any metal surfaces on the car until they are connected to the correct battery terminals. This can be more difficult than it sounds. Most areas under the hood are metal. If two people are available to jump-start a car, one person can simply hold the ends of the jumper cables safely separated, while the other person moves between the cars and makes the proper connections. One person can safely jump-start a car, but it does require close attention. With this in mind, here is a step-by-step guide to jump-starting a car.

10 steps for how to jump-start a car

It is always a good idea to consult your owner's manual for the correct order to connect the jumper cables. There may be variation among different car makes. Below is the most universally accepted method for jump-starting cars:

1. Choose a good pair of jumper cables or a portable jump starter

Keep jumper cables in the trunk for easy access. The cables should be thick, with adequate insulation and clean metal clamps. In some cases, the cables themselves will come with a chart reminding you of the proper order in which to connect them. If you have a jumper box, make sure the battery is fully charged before storing it in your car.

2. Open the hood of each car to locate each battery and its terminals

In some cases, the battery may be hidden or in the trunk, with remote positive terminal (+) and negative terminal (-) posts provided for jump-starting instead. Some vehicles may have a remote negative connection even if you can access the battery. This is for the final connection that we'll learn about later. Those with a portable jump starter can skip to step four.

3. Park the vehicle with the good battery close to the one with the dead battery

Leave yourself just enough room to walk between them. As you are hooking up the jumper cables, make sure the metal ends of the cables don't dangle into the engine compartment, where they could get caught on moving parts such as a belt or a fan, or on the outside of the car, where they could scratch the paint. Turn off the ignition in both vehicles, set the parking brakes, and make sure that the vehicles are in either park or neutral, depending on whether they have automatic or manual transmissions. Turn off all accessories, such as the lights, climate control and radio. If the vehicles are parked in a safe area, turn off the hazard flashers too.

4. Clamp one of the red positive (+) jumper cable ends to the dead battery's positive terminal

Be sure the clamp "bites" onto the battery terminal to provide a strong electrical connection. If there is corrosion on the terminal, twist the jaws of the clamp until it cuts through the corrosion and into the metal. Before moving on to the other car to make connections, make sure the matching black cable clamp is not touching any metal surfaces. Now clamp the other end of the positive jumper cable to the positive terminal in the booster car. Again, confirm that a plus sign is next to the battery terminal. Those with a portable jump starter can skip to step seven.

5. Connect the black negative cable end to the negative (-) battery terminal in the booster car

Now that the negative cable is connected to the battery terminal, you can attach the other end to an unpainted metal surface on the engine of the car with the dead battery. If a labeled remote negative terminal is available, use it. Otherwise, find an unpainted bolt or bracket that is at least several inches away from the dead battery. This will provide a solid electrical grounding and further reduce the possibility of sparking.

6. Confirm that the jumper cables are not near any moving engine parts and start the booster car

Let it idle for several minutes to build up a sufficient charge to start the other car's dead battery. If the dead battery is new and was drained by the car lights being left on for an extended time, it will probably start quickly. If the battery is old or if the car sat parked for a long time (about a month or more), it may take longer for the battery to charge and start. It sometimes helps to rev the engine in the booster car a little to hurry the process along.

7. Start the vehicle with the dead battery and let it idle for a few minutes

Those with a jumper box should make sure the unit is turned on first and a confirmation light appears. If the vehicle won't start but it does crank quickly, then look for other problems, such as an empty gas tank.

8. Carefully disconnect the jumper cables, reversing the connection order

The first cable you remove (the negative terminal on the formerly dead battery) is the most critical. Make sure your helper holds the cable away from any metal or the other cable ends while you disconnect the others.

9. Drive the jump-started car for at least 20 minutes so its alternator can recharge the battery

Make sure you are somewhere safe and the car is in an easy-to-access location before shutting off the engine. The car might need to be jump-started again depending on the battery's condition or the health of the alternator.

10. If the battery that you've jump-started is more than 3 years old, consider having it tested at an auto parts store

If other problems in the car caused the dead battery, such as a bad alternator or starter, take the vehicle to a mechanic for an inspection.

FAQs

What is the correct order to attach jumper cables?

Check your owner's manual for the proper order of attaching jumper cables, but in general, the order should be: red to the plus terminal on the dead battery, red to the plus on the working battery, black to the negative terminal on the working battery, and black to an unpainted piece of metal under the hood of the dead car.

What is the "mnemonic" for jump-starting a car?

The rhyming reminder, or "mnemonic," for jump-starting a car goes something like this:

"Red from the dead to red on the good. Black from the good, to under the hood."

This is an easy way to learn the order to get started, but it doesn't address the clamps to remove first. Here's our mnemonic for this step: "When the battery's not dead, remove black then red."

What should you always remember when jump-starting a car?

Important things to remember when jumpstarting a car are to know the proper order of attaching the cables and make sure that the second black clamp is grounded to an unpainted piece of metal. You also want to avoid the clamps making contact with each other (or other parts of the engine) when connected to a live battery.

What do you take off first when jumping a car?

The first item to remove when jumping a car is the black clamp, attached to the negative post, on the vehicle being jumped. Have someone hold that cable, or set it on the ground, making sure it does not touch the red cable or anything else under the hood. Do the same for the black clamp of the donor vehicle, then remove the red clamp from the positive post on the formerly dead car battery, ensuring the clamps do not make contact with each other.