How to Jump-Start a Car Safely

How to Jump-Start a Car Safely bb3 Dec 30, 2013

By Staff Writer State Farm™ Employee

  • Email
  • Print

Being stranded in a car that won't start can result from many issues, but if your problem is a worn battery, you can be back on the road with a little help and some good planning. All you need is a jump-start. But you don't need to be a mechanic or even a "gear head" to do it you just have to know how to jump-start a car safely.

Diagnose the Problem

Just because your car has trouble starting doesn't necessarily mean it's a failed battery. Here are some ways to tell if your car has a dead battery.

  • Listen to your engine. If you hear only a clicking sound when you turn on the ignition, or the engine turns slowly, your battery may be the problem.
  • Test with your lights. Another test is to turn on the headlights and interior lights, then turn the ignition key again. If the battery is low, the lights will dim significantly.
  • Get your car checked. If your engine is turning normally and the lights are not dimming, your battery may not be the problem and a jump-start will not help.

Safety First

Jump-starting a car can be very dangerous and cause serious injuries. According to the Sight and Hearing Association, each year nearly 6,000 motorists suffer serious eye injuries, even blindness, because of improperly jump-starting a dead vehicle battery. Injuries can be caused by battery explosions, chemical burns, crush injuries from lifting or dropping the battery, and electric shock from battery and/or post contact.

If at any time you're not comfortable with the procedure, call an emergency roadside professional service. If you have an emergency road service option with your insurance company, call them and ask for assistance.

If you decide to jump-start your car, make sure you're prepared with the right equipment on hand.

  • Read your owner's manual. Some manuals have specific procedures on how to jump-start their vehicles. They also include information about the location of the battery, which may not be in the front of the engine as is usual. Some manufacturers do not allow jump-starts; you could void your warranty if you attempt to do the procedure.
  • Use high-quality cables. Make sure your jumper cables are tested and approved by the Society of Automotive Engineers (SAE), are in good condition, color coded, and at least 12 feet long. Cables in poor condition can cause sparks, fires, and be dangerous to the person jump-starting the car.
  • Wear gloves and eye protection. All vehicle batteries contain sulfuric acid and produce hydrogen and oxygen gasses. Batteries can explode and cause fires in an instant.
  • Make sure you can see everything. Many things spin under the hood of your car when it's running, so it's important that you can see everything that you're working on. Have a flashlight shining on your engine bay to make sure that cables and anything else are kept out of harm's way when the engine turns over.

Prepare Both Vehicles

Once you've found a running vehicle to provide the jump-start, you need to make sure everything is prepared before hooking up the cables.

  • Make sure the cars are not touching. Park close enough for the cable to reach both vehicles' batteries, but not so close that they touch. Cars that are touching can create a shock.
  • Turn off all electrical devices in each car. That includes the radios, heater fans, and any accessories that could put a drain on the battery when the car starts.
  • Turn the ignition to "off" on both vehicles. This prevents any electrical overloads on the cars when you connect the two batteries.

Hooking Up the Cables

With both engines now off, it's important to hook up the cable in the right places, and in the right sequence.

  • Put on eye protection and gloves.
  • Light up the engine bays of each car.
  • Identify the positive (+) battery terminal and the negative (-) on each car. Make sure to double check this before you attempt to connect the cable. Reversal of polarity can cause serious damage to the vehicle and it's electrical system.
    Use a rag or steel brush to clean off the terminals.
  • Prepare the cables for connection.
    • Lay the cables on the ground, making sure the clamps aren't touching each other.
    • Connect a red cable (positive) to the dead car's positive (+) battery post.
    • Connect the other end of the red cable to the live car's positive (+) battery post.
    • Connect the end of the black cable (negative) to the live car's negative (-) battery post.
    • Do not connect the other end of the black cable to the dead car's negative battery post. Instead, locate an unpainted metal part of the dead car's engine, away from the battery. Look for a large bracket or bolt, but be careful not to put it near a part that will be spinning once the engine starts up.
  • With everyone away from the open hoods, start the engine in the live car first.
  • Wait a few minutes, and then try to start the dead car.
    • If you don't get any improvement in the dead car, turn everything off and check the connections again. Clean the posts of the batteries and wipe off the area where you are connecting the black cable to the dead car.
    • Start the live car again. You can raise the idle a little to help with the charging, but don't race the engine.
    • Start the dead car again.
    • If the dead car still doesn't start, turn off the live car, remove the cables in the reverse order (see below), and call for a tow truck. Your problem may be more than just a dead battery.
  • If the formerly dead car starts, leave both cars running for a few minutes, then remove the cables in the opposite order.
    • Disconnect the black cable (negative) connected to the formerly dead car.
    • Disconnect the black cable (negative) to the live car.
    • Disconnect the red cable (positive) connected to the live car.
    • Disconnect the red cable (positive) connected to the formerly dead car.
  • Leave the formerly dead car running for at least another 20 minutes to help recharge the battery.

Portable Jump-Starters

Another option is a portable jump-starter, which is a battery device (usually containing a non-spillable AGM battery) you keep in your car that can be recharged and used again. They can either be a larger device that clamps to a car's battery, or a smaller device, which plugs into a car's power outlet. They're convenient to have, but they must be periodically recharged even if they're not used because they lose their charge over time.

If everything goes as planned, you'll be back on the road and traveling. To cut down on the chances of this happening again, it's a good idea to visit a qualified service station or auto parts store to test your battery. If your battery is old and tired, the jump-start may just be a temporary solution until you can replace it. Also, make sure to check your emergency road kit to make sure you're prepared for the next roadside problem.

Additional Reading:

Car Talk: Official Car Talk Guide to Jump-Starting Your Car

wikiHow: How to Jump Start a Car

Sight & Hearing Association: Battery Safety

Consumer Reports: Portable jump-starters

If you are commenting using a Facebook account, your profile information may be displayed with your comment depending your privacy settings. By leaving the 'Post to Facebook' box selected, your comment will be published to your Facebook profile in addition to the space below.


Find a local agent below

Get a Rate Quote Now