Jumper Cables - How to Jump-Start a Vehicle

"Click-click-click… click-click-click." Then, dead silence. The engine won't start. Needless to say, it can be a nerve-wracking experience to be stuck on the side of the road with a dead battery.

Even though jump-starting a dead battery is an easy thing to do, many people rely on a road service provider or an altruistic motorist.

Rather than waiting around for a tow truck or somebody with the right tools, learn the safe and proper way to jump-start a dead battery. And with today's portable jump starters— sometimes as small as a cell phone—it's easy to bail yourself and others out without having to flag someone down.

What to Do Before Jump-Starting a Vehicle

Check the owner's manual for specific instructions related to your vehicle. For instance, if your battery is in an odd location, such as the trunk or wheel well, you may have to connect the cables to a different area, such as a junction block. Regardless, it's always a good idea to follow the instructions in your owner's manual.

Your "dead battery" may just be a "dirty battery." Sometimes, the battery won't work because of dirty terminals and loose connections. Try cleaning the battery terminals with a stiff brush dipped in a baking soda and water mixture.

Never touch the terminals with your hand as sulfuric acid may burn you. It's always a good idea to wear protective gloves and glasses when you are working on vehicle batteries. If any powdery stuff gets on you, clean it off with soap and water immediately.

Rinse the terminals with a spray bottle of water, wipe dry with a rag, and tighten the connections with a wrench. Turn the ignition to see if that did the trick before attempting the jump-start process.

Important Safety Tips:

  • Make sure there are no open flames or cigarettes in use while working on a battery. Batteries emit very flammable hydrogen gas.
  • Always inspect the battery for damage before proceeding. If you notice leaks, cracks, or any other damage, don't take the risk trying to jump start the car. Instead, call roadside assistance or a tow truck.
  • Make sure the red and black ends of the jumper cables never touch each other once they are connected to a battery. This can result in a very dangerous electrical arcing situation that can cause damage to people and vehicles.
  • Don't let your jumper cables hang loose around the engine. They can potentially interfere with moving parts.
  • Make sure both cars are off with the keys removed before connecting the cables.
  • Red = Positive (+); Black = Negative (-)
  • Purchase only heavy-duty, high-quality jumper cables. Avoid "cigarette lighter jump starters." They take a lot of time to generate any useful charge, and only if you are lucky will they work.
  • Make sure the clamps are firmly in place to avoid them being shaken loose and possibly causing an electrical arcing or shorting situation.
  • Keep your face away from the batteries at all times.
  • Never cross cables when they are attached to a battery. If the clamps contact each other while connected to a battery or jump starter, a spark can cause a battery explosion.

Battery explosions are rare, but possible

Hydrogen gas is produced as a natural byproduct of the chemical process used to create electricity. Although there is no real danger of electrocution since the voltage is fairly low (about 12), small sparks can cause explosions from the hydrogen gas that is produced by the battery.

According to The Straight Dope, there may be 6,000-10,000 injuries caused by exploding car batteries every year. While these numbers were never confirmed, it's still a real danger that affects a significant number of people every year.

Although the chances are slim, you can avoid battery accidents by following the above safety tips and the proper procedures below.

How to Jump Start a Vehicle (with Jumper Cables)

You will need jumper cables (plus another vehicle). We also recommend gloves and glasses for protection, and baking soda, water, a wire brush and rag to clean off battery terminals (if necessary).

  1. In addition to jumper cables, you will need another vehicle to provide the jolt of power from their working battery.
  2. Have the person with the good battery pull up to the disabled car with both engines facing each other. Make sure the vehicles are close but not touching. If the cars are touching, a dangerous arc can be produced.
  3. Turn off both cars, remove the keys from the ignition, and pop the hoods.
  4. Locate the positive terminals (marked by a "+" or POS sign) and negative terminals (marked by a "–" or NEG sign). If you can't find your battery, check the owner's manual.
  5. You may need to remove terminal coverings, known as cell caps. These may be individual caps for each terminal or a yellow strip that can be peeled off. Keep in mind that your battery may not have cell caps.
  6. Make sure both cars are completely off and both batteries are in good shape (no cracks or leaks, for example).
  7. You may have to clean battery corrosion off of terminals and cables to establish a clean electrical connection. Dip a wire brush (or old toothbrush) into a baking soda and water solution to clean up corrosion. Rinse clean with a spray bottle of water and wipe dry with a rag. Try not to get any water or baking soda into the vents of the battery.
  8. Connect the jumper cables in the following order:
    1. Connect the red jumper cable to the positive terminal (+) on the dead car's battery.
    2. Connect the other end (also red) to the positive terminal on the working battery.
    3. Connect the black jumper cable to the negative terminal (-) on the working car's battery.
    4. Connect the other end (also black) to a clean, unpainted metal surface under the disabled car's hood (the engine block is a good place).
  9. Do NOT connect the black end to the negative terminal on the dead car's battery! This can risk causing a spark that can ignite the hydrogen gas surrounding the battery.
  10. Start the working car's engine and let it run for about 2-3 minutes. This charges the battery.
  11. Then, start up the disabled car. If the engine does not start, turn off both vehicles and wiggle the clamps to try to establish a good, clean electrical connection. If you cannot get the car to start after a couple of tries, you may need to have your battery replaced or the car towed.
  12. Once the dead car's engine is running, remove the jumper cables in the opposite order that you put them on:
    1. Disconnect the black clamp from the grounded metal section of the dead car.
    2. Disconnect the black clamp from the good battery.
    3. Disconnect the red clamp from the good battery.
    4. Disconnect the red clamp from the dead battery.
  13. After a successful jump, run the vehicle for at least 15 minutes so that the alternator has time to charge the battery.

If the battery dies soon after jump-starting the vehicle, it's probably due to a dead alternator not being able to charge the system.

How Long Does a Car Battery Last?

Car batteries last around 3-5 years. If your battery is older than three years, it's a good idea to get it professionally tested every year.

Many auto shops, battery centers, and tire stores will do this for free and it only takes a few minutes. They'll be able to tell you if a new battery is necessary and roughly how long your battery will last.

Click here for more car maintenance essentials.

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