How to Jump a Car, According to the 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’s a few reminders before we get into the proper way to jump a car.
- Don’t try the ignition again.
- Switch off headlights, air conditioner, wipers, everything electronic.
- Get jumper cables or a portable jump starter.
- Park the other car near yours, not touching, and turn it off. You don’t need another car if you have a jump starter.
- Take off any jewelry.
- Get gloves and eye protection. Sunglasses will do in a pinch.
How to Jump a Car in 5 Steps
- Attach the red cables first, starting with the good car. Clamp to the cars’ positive posts, usually red but not always.
- Attach the black cables, one to the good car’s negative post and the other to an unpainted surface on the dead car. Not the dead car’s negative post.
- 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.
- Detach the black cables. Start with the car you jumped.
- Detach the red cables. Again, starting with the car you jumped — and make sure they don’t touch each other or anything else.
Once you have the car going again, don’t bother trying to recharge it 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 revive the battery a little.
However, the damage might be done.
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.
Jumping a car is easy, but it’s only a temporary fix.
Instead, go to the nearest repair shop or favorite battery store. Ask for a comprehensive charging and electrical system test. A battery test can identify whether you need a professional auto repair or a simple battery replacement.
When you get a jump, you need a new battery.
Is it time for a fresh start? Visit one of our Interstate All Battery Center locations for a free battery test to find out.
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 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.
- Get a battery 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.
Dead batteries can surprise you any time.
Instead, get a battery test, available wherever Interstate is sold, to replace batteries before they die. You may never need a jump again.
What If My Car Still Won’t Start With Jumper Cables?
Wait 10 minutes if your car won’t start when you try to jump it. Leave it connected to a car that’s running, and rev it up to 2,000 rpm. The other car’s alternator may charge the battery a little bit, but don’t expect much. An alternator is not a battery charger. You may blow a gallon of gas to put a 1% charge into a weak car battery.
Even then, your battery might be so dead that it stops the current from the good car from getting to your starter. Dead batteries don’t conduct electricity well. You’d know the battery is too weak if the dashboard lights turn on, but they fade in less than a minute.
Otherwise, a battery might not be why your car won’t jump start. Instead, it 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 and it doesn’t start.
How to Jump a Car Without a Negative Terminal
You might find a car battery under the hood when you need to jump an Audi, BMW, Mercedes-Benz or Volvo. More than 35% of the cars on the road in 2022 had a battery tucked away in a difficult-to-reach spot: behind the wheel well, under the back seat, in the trunk, etc.
Instead of a battery under the hood, you’ll find a red cap with a positive sign.
A remote terminal is a direct line to the positive post of your car’s battery, wherever it is in the car. The terminal is in the engine compartment precisely for jumping a car when the battery is somewhere else.
Here’s the proper way to jump a car from its remote terminal:
- Attach the red cables first, from the good car to the remote terminal on the dead car.
- Attach the black cables, from the good car’s negative post to an unpainted surface on the dead car.
- Start your engines.
- Detach the black cables, starting with the unpainted surface.
- Detach the red cables, starting with the remote terminal and then the good car.
Then go get a battery test.
Do not give a jump start with your Audi, BMW, Mercedes-Benz or other vehicle with a remote terminal. If your car has only a positive post in the engine compartment, you should not offer a jump. Yes, you could spend the time disassembling your car to find the battery — but it’s no longer safe to jump a car. The access you do get will be narrow without much room to keep the clamps safely attaching to what they should and touching nothing else.
Ask for a free battery check at any of these 150,000 locations
Où pouvez-vous effectuer une vérification de batterie gratuite près de chez vous? Put in your city or ZIP code, and we'll show you dozens of locations nearby. Ou recherchez notre logo chez n’importe quel atelier de mécanique près de chez vous.
Also, an electric car cannot jump a gas car. If you’re driving any EV, do not try to jump another car.
In both cases, the best way to be someone’s good Samaritan is with a portable jump starter battery.
How to Jump a Car with a Jump Starter Battery
Jumper packs, jump starters or booster batteries are a compact, rechargeable battery designed to jump a car themselves. They come in various sizes from a handheld brick to the size of a large tote bag. Some have outlets for recharging phones and tablets; others only come with big clamps.
- Turn car electronics off. Especially the heater, air conditioner and headlights. Otherwise, you’ll be using the battery’s power to run those instead of using its power to start the engine.
- Attach both cables, red first. Depending on the model, your jump starter may have indicator lights to show when you have a good connection.
- Start your car. If it doesn’t immediately start, disconnect the jump starter.
- Detach the cables and recharge the battery. Make sure you also go get a battery test.
Jumper packs are the safest way to jump a car — whether you have a remote terminal or not.
A lot can go wrong for either car when you jump a car. A voltage spike in one can send too much power into the other, potentially damaging power control circuits that govern the alternator, starter and other electronics in the engine. If more than 15 volts go into your engine, you could permanently damage the onboard electronics in ways that’ll baffle most automotive electronics experts.
A portable jump starter battery only has 13 volts, low enough to protect your car from any overloads.
How to jump your car without a second car!
Is your car battery dead? Connect this handheld battery designed to jump start your car and get going again. Charge your phone, laptop and anything else when you don't need a jump.
These portable batteries offer a fast, safe, handy and cost-effective alternative to connecting two cars and their electrical systems. They also work well in an emergency kit. After all, the only time you would know you need to jump a car is when you’ve got places to go.
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 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.
Speaking of dead batteries, why is your phone dying so fast?
It may be time to replace the battery in your phone. Interstate All Battery Center offers mobile device repair in select locations.
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. However, 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.
However, 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.
You May Not Need to Know How to Jump a Car
You don't need to wait for a battery to fail before you replace it.
It’s entirely possible to avoid getting a car dead battery. It’s even likely you may not ever need to know how to jump a car as long as you get your car battery tested twice a year. 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.
As soon as your mechanic says you have a weak battery, replace it.
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.
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