How to Jump Start a Car Battery

If it hasn't happened to you already, it likely will someday: Your car stalls on the side of the road and you suspect you've got a dead battery. This can happen for lots of reasons.

A common culprit is a weak battery, a bad alternator or worn-out alternator belt that will need to be replaced or repaired. But it also can be as simple as headlights, or an interior light, left on that caused the battery to drain overnight. Whatever the case, you need to jump start the battery to get your car to a safe spot for further examination. Here's what you need to know about how to jump start a car.

Car Ownership 101

One of the first lessons is to carry jumper cables. One of the second lessons is to know how to use them.

A portable jump starter is also a good option. When you get a new car, make sure your battery cables get transferred to the trunk. When your kids learn to drive, teach them this stuff.

While you're at it, you should be able to pop the hood of your car and identify the engine and the battery, so you know what to touch and what not to touch. Some cars have their batteries somewhere else, like in the trunk. Better to know this now than to be caught off-guard in a stressful emergency situation.

Step 1. Prep Both Cars

So now you're on the side of the road with a dead battery, but you're not flying totally blind. You'll get through this, and you have a friend or a generous stranger ready and willing to help.

First, park the car with the dead battery close enough to a working car (booster car) so the jumper cables can reach both batteries. Turn off the ignitions and set the parking brake on both cars. Turn the lights, radio and other accessories off both cars. You don't want either car's battery sending any power to anything.

Step 2. Connect the Jumper Cables

Open the hood of each car to locate each battery and its terminals. Locate the positive terminal and negative terminal on your car battery. The positive post is often red, but it's not always, so look for the plus or minus sign to determine the battery post's polarity.

Jumper cables also are red and black (or positive and negative). The red clamps attach to the positive battery terminals and black clamps attach to the negative battery terminals. Touching the wrong cable to the wrong battery terminal could create a spark, or you could get a nasty electrical shock, so be sure to connect the cables in the proper order:

Connect one end of the red positive jumper cable to the dead battery's positive terminal.
Connect the other end of the red positive jumper cable to the positive terminal of the good battery of the booster car.
Connect the black negative jumper cable to the negative terminal of the good battery in the booster car.
Connect the other end of the black negative jumper cable to an unpainted metal surface like a bolt or bracket at least a few inches away from the battery of the dead battery.

Double-check Everything

Given the potential for injury to both you and your car, glance over your setup and ensure the jumper cables are properly secured, and away from any moving engine parts. If so, it's time to safely jump start the dead car battery.

Step 3. Jump Start the Cars

First, start the booster car and let it idle for several minutes.

Next, start the car with the dead battery and let it idle so the battery can recharge. If the car doesn't start right away, you may need to wait a few minutes until the battery is fully charged.

Finally, once the dead car is running and the battery has a sufficient charge, disconnect the jumper cables in the reverse order you connected them. It's especially important to be careful here, since the car is still running. Don't let the cable ends touch anything, especially metal or the other clamps.

Drive the car for at least 20 minutes to allow the alternator to recharge the battery. Don't turn the car off until you're somewhere safe, in case the charge doesn't hold. If your battery is more than a few years old, you might want to have it tested or replaced.

A Note About Hybrids

If you drive a hybrid vehicle, or have a lot of friends who do, you should keep in mind that the process to jump-start a hybrid car is a little different.

Whether you're jump starting your own car or think it's likely you'll be called upon to help out a pal, it's worth remembering that hybrid cars might look a little different under the hood, and it's especially important to ensure you're connecting the jumper cables to the right battery.

Check, double-check and triple-check everything before you crank the engines, and you should be good to go.