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How to Jumpstart a Car

The Safe Way to Use Jumper Cables

Average Repair Cost & Time
Avg. Repair Time
10 minutes

Difficulty Level

Beginner
Expert

Overview

It happens to everyone at some point. Headlights were left on in the parking lot. The dome light was left on overnight. The trunk lid stayed open for too long. Now the battery is weak and your car won’t start.

The simplest and cheapest way to get your car running again is to jumpstart it with another vehicle. An alternative would be to use a jump-starter, a portable battery box used to jumpstart a car. As mentioned in the video, the procedure is essentially the same, but with a jump-starter you do not need a running vehicle. This article will cover jumpstarting your car with a vehicle that is running.

While this job does not require a lot of tools or experience, it is important that you make sure to use proper equipment and procedures to prevent injury to yourself – or damage to your car.

Parts & Tools Required

Tools:
  • Quality set of jumper cables
  • Wire brush
  • Gloves
  • Safety Glasses
  • Optional: Battery Jump Starter (instead of second vehicle)

Before You Begin

Before you attempt to jumpstart your car, make sure that the battery is really the culprit by performing some simple tests. Turn the headlights on (you may have to turn the key on for some cars) and see if they are bright or dim. If the headlights are bright, your battery is probably not the problem; if the headlights are dim, it is a good chance that the battery is low.

Also, look at the dash lights and turn on the radio. If the dash lights are bright and the radio works fine, your battery might be working properly and the problem could be a blown fuse or a faulty ignition switch. But if the dash lights are dim or flickering and no sound comes from the radio, the battery is probably going bad.

Next, turn the ignition to crank the engine. If the engine turns over quickly, the battery is strong. But if the engine cranks slowly or not at all, or if you hear a clicking sound, the battery is probably weak.

Finally, check the cables going to the battery for signs of wear, and make sure the battery terminals are clean – a wire brush can be helpful here – and secure. A poor connection can cause symptoms of a weak battery. (Refer to our article How to Clean Battery Terminals for more information.)

Remember to keep your hands, any loose clothing, and jewelry away from moving parts of the engine where they could get caught and cause serious injury. And while a car battery does not present a high level of danger from electric shock, rings or watches that come in contact with the positive battery terminal and any other metal in the engine compartment at the same time can cause a serious burn.

Also, do not smoke while jumpstarting a car. A battery gives off gasses that are explosive, and the presence of fuel vapors from the engine is always a possible fire hazard. Do not lean over the battery; if there is an accident you do not want to be hovering over the source of the problem. And be aware of anyone who might be in the area.

When Not to Jump Start a Car

If the battery shows no signs of life and the temperatures are below freezing, do not attempt to charge or jumpstart the battery. A fully charged battery will not freeze, but a battery that is considerably weak or completely dead can freeze. Jumpstarting a frozen battery could lead to explosion.

Safety should always be a concern, even with a simple repair. If possible, use personal protective equipment such as a pair of gloves to protect your hands. Shield your eyes with safety glasses or goggles.
Image courtesy of consumerreports.org

Likewise, if the battery is cracked or leaking, hydrogen gases leaking from inside the battery can ignite with just a spark and cause the battery to explode.

Read the owner’s manuals for both cars. Some vehicles require additional steps before jumpstarting; some vehicles are not allowed to be jumpstarted at all without voiding the manufacturer’s warranty. It may be necessary to check the owner’s manual of the running vehicle for the precautions as well.

Please read and understand this Legal Disclaimer.

Once you have determined that a weak battery is the problem and you have ensured your safety, you are ready to begin.

Locate the Battery

Find the battery in each vehicle. Most batteries are in the engine compartment and can be easily accessed by removing a plastic cover.

But some batteries are difficult to reach or are located in a different part of the vehicle – in the trunk or in a fender well. In those cases, the manufacturer will likely have provided a pair of electrical contacts or lugs in the engine compartment for the purpose of charging or jumping the battery. Refer to the owner’s manual or a repair manual for the battery location and specific jumper cable attachment instructions and precautions.

(On some vehicles the battery is found in the trunk or in a fender well)
(Alternate negative ground lug on engine)
(Alternate positive lug in engine compartment)
(Alternate positive lug in engine compartment)

Make sure that the voltage of both vehicles is the same. The majority of cars and trucks on the road since 1956 have a 12 volt system, but some older cars were 6 volt, and some newer heavy duty diesels have 24 volt systems. Newer electric and hybrid cars have systems that store significantly higher voltages, but these systems are not likely to be accessible for jumpstarting cars. If a hybrid vehicle has a car battery for starting the engine, it will most likely be 12 volts. Check the owner’s manual to make sure.

Position the Vehicles

When jumpstarting your car with another vehicle, position the cars close together. Make sure that the vehicles are not touching and that the jumper cables will reach between the batteries.

Cheap jumper cables are often made with lighter gauge wire and thinner clamps than quality jumper cables. Since the cables are designed to transmit electrical current, the higher the quality, the more current they can transmit – and the more power your weak battery will receive.

Place both vehicles in park or neutral with the parking brakes set to prevent them from accidentally rolling while being serviced. Turn off the radio, the wipers, the headlights, and any other power accessories on your car. It is wise to disconnect electronic devices – cell phones or GPS units – plugged in to 12 volt sockets to prevent damage from any power surge that might occur while jumpstarting the car. Both vehicles should be turned off and the keys removed at this point for safety.

Attach the Jumper Cables

Locate both the positive and negative terminals on the battery (or the alternate terminals or lugs recommended by the manufacturer). The positive elements of the system will be signified with a (+) and the components will usually be colored red. The negative elements will have a (–) and are usually colored black.

It will also be necessary to determine a separate negative ground location on the vehicle with the weak battery for the negative cable clamp in order to avoid a spark when making the electrical connection.

Attach one positive (red) jumper cable clamp to the positive (+) terminal of the weak battery. (Leave the negative cable clamp disconnected for now).

Do not touch the cable clamps to anything but the correct contacts. Also, pay attention to signs of a leaking battery and smells of acid or fuel. A spark could ignite any hydrogen gas or fuel vapors that might be present.

Attach the other positive jumper cable clamp to the good battery, followed by the negative (black) clamp to the negative (–) terminal on the good battery.

Lastly, connect the negative (black) jumper cable clamp to a bare metal spot on the engine or body of the car with the weak battery, as far from the battery as possible and away from sensitive electronic components. This will prevent accidental sparking near the battery that could ignite hydrogen gasses emitted by the battery and cause an explosion.

Make sure that the jumper cables are not touching any parts of the engine that will be moving (belts or pulleys) when the vehicle starts.

Jumpstart the Car

With the jumper cables connected and the area cleared, start the vehicle with the good battery and allow it to run for a few minutes to charge the weak battery. (It might be necessary to wait longer if the vehicle is significantly smaller in size than your vehicle).

Start your car. If your car does not turn over quickly enough to start, turn the key to the off position and allow the battery to charge for an additional five minutes before trying again. It may be helpful to rev and hold the running vehicle at 2000 rpms to help with charging the weak battery. It may also be helpful to change ground locations to provide a better connection. This is where a quality set of jumper cables proves better than a cheap set.

If your car starts, remove the negative (black) clamp from the vehicle with the weak battery, followed by the positive (red) clamp.

Do not to allow the clamps to come in contact with one another while the cables are still connected to a battery, otherwise a short circuit could cause damage to the vehicle or personal injury. While the voltage in a car battery is not high enough to provide a serious electrical shock when you touch the battery posts with your bare hands, if the cable clamps come in contact with one another, or if any metal contacts both the positive and negative terminals (like a wrench or screwdriver), damage or injury could result.

Lastly, remove both the negative and positive clamps from the good vehicle

If your car refuses to start, the battery might be too low to jumpstart. In that case it will be necessary to recharge or replace the battery.

3 User Comments
- Mar 07, 2017
I've been jumping cars (my own and other people's) since I was a wee lass of 16... and I still learned something. One thing I've learned the hard way is to always keep a good pair of jumper cables in my car, and to make sure they're long cables (20 feet or longer, and no, I don't get residuals from recommending these even though my last name is Long). These help ensure I can get myself out of any kind of jam, even if the other car isn't able to get really close to me because of where/ how I am parked.
- Mar 07, 2017
Super helpful information! I have recently had to jump my car and was a little concerned that I didn't injure myself. True story. I appreciate the "Safety Tips". Thanks RepairPal!
- Apr 24, 2017
True. there will be a day when you're parked facing in and , say you drive a Suburban, short cables just wont do it in the time of need! I bought a Rally Jump Starter.It has an internal 12 volt battery so you wont need a stranger's car. It also charges with a car cigarette lighter (DC voltage), Home charger (AC voltage) and an emergency pull handle that charges (enough to turn on a car) the unit with just 3 minutes of pulling the handle. Also has an air compressor (with gauge) for putting air in tires, usb plug, a 115 volt outlet (perfect for the beach, camping or inside your truck to connect a Playstation), 12 volt outlet, emergency/work led light. Also, the jumper cables have an on/off switch and are of good quality. I bought it on ebay for around 100.