How to Jump a Car With Jumper Cables, According to the Car Battery Experts

If you're asking how to jump a car, you're probably having a stressful day. So, let's cut to the chase.

Here are a few reminders before we get into the proper way to jump a car.

• If you hear a clicking noise, stop. Don't try the ignition again.
• Switch off headlights, air conditioner, wipers, everything electronic.
• If the dead vehicle has a manual transmission, shift it into neutral and pull the parking brake.
• Park the other car near yours, not touching, and turn it off. (You don't need another car if you have a jump starter, also called a jump box.)
• Take off any jewelry.
• Get gloves and eye protection. Sunglasses will do in a pinch.

5 steps to jump-start a car with jumper cables

1. Attach the red clamps first, starting with the good car. Clamp to the cars' positive terminals, usually red but not always.


2. Attach the black clamps – but only one goes on a battery. Connect one black clamp to the good car’s negative battery terminal. You should clamp the other on a metal component like a bolt or a bracket, not the dead car’s battery.


3. Start the cars, good car first. Moment of truth. If the dead car doesn’t start at first, give it a few minutes before trying again.


4. Detach the black clamps. Start with the dead vehicle.


5. Detach the red clamps. Again, starting with the car you jumped — and make sure they don’t touch each other or anything else on the engine block.

Jumping a car is easy, but it’s only a temporary fix.

Once you have the car going again, go to the nearest repair shop or your favorite battery store. Ask for a comprehensive charging and electrical system test. A healthy car battery should have 12.6 volts or more. However, a simple voltmeter or multimeter won’t tell you how much internal resistance has built up in your battery. For that, you need a battery test.

A battery test can identify whether you need a professional auto repair or a simple battery replacement.

How long does it take to charge a car battery with a jump start?

Jump leads do not charge a battery. Here’s why: All that power to jump-start the engine goes straight to the starter. It passes through the dead battery and doesn’t stay. Instead, it spreads to the rest of the car’s systems.

You might think you’re recharging the dead battery by leaving the leads connected and revving the engine. Instead, you’re risking damage to both cars because you’ve linked both alternators. Alternators send power to the rest of the car, so revving the engine raises voltage a little bit, but not nearly enough to tell the alternator to charge its battery. Instead, you’re just making the dashboard lights glow a little brighter while spending a lot of gasoline.

Now, you could recharge the jumped car by driving. To charge a car battery by driving, you’d have to drive for hours at highway speeds and strain the alternator in the process. If you have a battery charger or trickle charger, you might be able to recharge the battery a little.

That said, the dead battery might be too damaged to take a recharge.

Sitting with less than 50% charge for just a few hours will shorten a battery’s total lifespan, if not ruin it right then. Car batteries start losing their ability to store power if they’re not fully charged. That’s why your car battery might be dead after sitting five days.

On top of that, your car’s onboard computers have lost their memory. It’s just as if you disconnected the battery without a memory saver. So the engine's idling behavior may turn erratic, transmission shifting gets rough and a few other issues may pop up until your car's computers rebuild their data sets.

Safety Checklist Before You Jump Start a Car

Jumping a car is simple, but also potentially hazardous. Let’s talk about how to jump a car safely.

• Take off jewelry. Rings seem like an obvious hazard, but a necklace or bracelet can be just as dangerous.


• Put on gloves and glasses. Safety glasses or sunglasses, nitrile or cloth gloves — you should always protect your eyes and hands when you’re around an open engine.


• Inspect the battery connections. Corrosion at the posts can eat away at the terminals if you don’t clean it off. You might even need to replace the terminals before jump starting the car.


• Position the cars so they’re not touching. You don’t normally park cars like this anyway. However, it’s worth noting that you’re about to handle a lot of electricity. You don’t want the cars to touch because there will be an open circuit and that could potentially drain the good battery.


• Keep jumper clamps from touching each other. A spark from the jumper clamps could damage the power control module or any of a dozen onboard computers. You can use a simple rag or a red plastic cup to cover the clamps until you’re ready to connect them. You can jump a car in the rain, so long as you’re safely protecting the batteries and covering the jumper cable clamps.
  • Don’t let the clamps touch each other.
  • Don’t let the clamps drag on the ground or through water.
  • Don’t dangle the clamps. They might touch.


• Inspect the battery. Some obvious signs something is wrong with your car battery include:
  • Corrosion at the posts. Here’s how to clean corrosion off batteries.
  • The smell of rotten eggs. The battery may have been overcharged. Don’t try to jump the car.
  • Radiating heat. Another sign the battery has been overcharged. Don’t try to jump it.
  • Bulging or warped plastic case. A truly bad sign. The battery is not doing well. Don’t try to charge or jump it.
  • Frozen or cracked battery. A battery can be too cold to jump. If it’s frozen solid, do not try to charge it or jump it. You can warm it up, but it’s likely the case is cracked. Find a professional and get a replacement.


• Get an auto professional. If something’s wrong or you’re not confident you can jump a car safely, ask a qualified professional. They have the tools and training to handle problems you can’t anticipate when jumping a car.

What if my car still won’t start with jumper cables?

Disconnect the jump leads and explore some of the other reasons why your car won’t start.

It might not be the battery. Instead, the cause could be:

• The starter, if you hear clicking or grinding noises but the electronics turn on.
• The ignition switch, if the electronics turn on but there’s no sound at all when you try to start.
• The alternator, if electronics turn on briefly but fade out.
• A fuse, if the electronics turn on, the engine turns over and it still doesn’t start.

It is also possible the car battery is so dead that it’s blocking the jump-start.

Can a battery be too dead to jump?

Yes, your battery might be so dead that it stops the current from the good car from getting to your starter. Dead batteries, by definition, don’t conduct electricity well.

There’s one easy way to test if your battery is too dead to jump: Try to turn the electronics on.

If the dashboard lights turn on but fade in less than a minute, the battery needs to be recharged before a jump start will work.

In that case, you can connect the dead car to a running car and leave it for 10 minutes. Again, don’t rev the engine. An alternator is not a battery charger. You may blow a gallon of gas to put a 1% charge into a weak car battery.

Why Don’t You Connect the Negative Cable to the Dead Battery When Jump Starting a Car?

The dead battery will drag down the voltage of the good battery and it’s a potentially more hazardous jump start if you connect the negative jumper clamp to a dead car battery.

Every RV driver and golf cart owner connects batteries positive to positive and negative to negative because they want more amps for their 12-volt or 6-volt system. That’s a parallel connection. (If you connect batteries in a series, you get more voltage but the same amps.)

The problem is that batteries in parallel are only as strong as their weakest voltage, like a chain and its weakest link.

Well, if you’re trying to jump a dead car battery, that’s the weak link.

A dead car battery might have 11.7 volts. Meanwhile, a healthy car battery has 12.6-12.8 volts, and the entire electrical system with the car on might be running at 13-14 volts. As soon as the black jumper cable grips the negative terminal, the good car now has a dead battery on its circuit.

If the good car’s battery is extra healthy, you might jump a car just fine.

If the good car’s battery is average, you might not jump the dead car.

If the good car’s battery is a little drained or worn, the good car itself might not start.

So always connect the negative jumper cable to an unpainted engine surface, like the body or the frame. Not only does this work better, it’s safer. There’s a possibility the negative jumper clamp could spark on contact with the negative battery post. A spark alone can damage your computers, but if your battery’s been trying to charge (and there’s a little hydrogen gas in the air around it), you may have a bigger problem.

For your own safety, do not connect the negative jumper cable to the dead battery you’re trying to jump.

Yes, you can prevent dead batteries.

It’s entirely possible to avoid getting a dead battery if you get a battery test twice a year. Then, when a battery expert says it’s weak, replace it before it fails.

We recommend a battery test every six months or at least as often as your oil change. Car repair shops near you can test and identify weak batteries at risk of failing soon.

If you wait, you might have two months or two weeks left. What are the odds you’ll find your way to a repair garage in that time? If you’re too busy to replace it the moment a technician shows you the result, you might be too busy to return to a shop.

Instead of leaving it to chance, replace the battery before it dies.

Car batteries last for three to five years, but days of high heat can shorten their lifespan by drying them out and speeding up corrosion. Too many short drives without recharging on the highway can also deplete your battery, too.

Instead of draining your roadside assistance membership for a jump start, save those calls for a true emergency you couldn’t prevent.

Retire your weak car batteries before you even need a jump start.