How To Jump-Start A Car Battery

Skill Level:

The Jump-Start. While people have an idea of how it works, everyone is always asking the Part Pros how the professionals do it. That’s why we’re here to give you instructions and tips for reviving a dead battery the right way– an essential skill any time of year, but especially during the winter.

Remember, if you have any questions or if you're unsure of anything, feel free to contact the Parts Pros at your local PartSource. They're always ready to help, no matter what the job is.

Let's go!

Getting Started

Tools You`ll Need:
  • Jumper Cables
  • Hand & Eye Protection
  • A Functioning Car Battery to provide the boost

Make Safety Your Top Priority

Every vehicle is different. When it comes to maintenance and repairs, always follow the vehicle's owner's manual.

Safety should be your number one priority. Don't smoke, drink alcoholic beverages, or wear a necktie while working on the car. Watch out for hot objects, sharp instruments, hazardous materials and other potential safety hazards in and around your workspace.

Don't work with a Philips when the job calls for a flat. Substituting tools can compromise your safety or your vehicle's performance.

Finally, when the fun turns to frustration, or if the job requires specialized knowledge beyond your capabilities, please do not attempt it yourself. Talk to a Parts Pro or seek the assistance of a professional mechanic or installer. The last thing we want is someone getting hurt.

Before you Begin

The three major reasons for getting a dead battery in the first place:


    • Leaving your lights on
    • Not maintaining your battery properly with the correct water levels (for older maintenance batteries)
    • Breakdown of the diode bridge or voltage regulator in your alternator

Of course, some people get a bad starter, but the odds of that are low compared to the other causes.

Now, a few precautions:

Line both cars up so the batteries are as close as can be. Make sure the cars are in park and that both cars are turned off and not touching each other before you connect the cables.

Make sure all headlights, blinkers, car radios and A/C's are off, and cell phones are unplugged. Unplug all accessories from cigarette lighters and other power sockets from both cars.

Jump-starting a battery can crank 300+ volts through your system and the transients can destroy equipment. These voltage spikes are caused by inrush current into the inductances in your electrical system

Familiarize yourself with the Positive (+) and Negative (-) terminals of both car batteries so you know exactly which one is which. All batteries are clearly marked so if you can't find it, it's probably under 1/8" of caked-on corrosion around the terminals. Wipe off any battery acid that may have leaked.

IMPORTANT: If the battery is cracked and liquid is leaking out, DO NOT go any further! Bite the bullet and go buy another battery and swap it out. If you try to jump start a battery with a crack in it, it will explode.

Try to clean off any corrosion around the dead battery terminals. If you have tools, loosen the wires from the terminals, clean them off, and then re-tighten the wires to the shiny posts. Corroded posts prevent the power from getting through the cables and into your battery to revive it. If you have a file handy, try to file the metal battery posts until they are nice and shiny. In a pinch use pliers to clamp down and scrape off corrosion too as the metal is somewhat soft.

Usually the Positive(+) battery cable is red or orange, and usually the Negative (-) or ground cable is black, but always check to be sure.

STEPS FOR Connecting the Car Battery Jumper Cables
  • 1:
    The cables must be connected in the exact order listed below. If possible, wear personal protective equipment such as eyewear and gloves, as batteries can be dangerous.
  • 2:
    Connect one end of the Positive(+) cable to the Positive(+) post of the dead battery.
  • 3:
    Connect the other end of the Positive(+) cable to the Positive(+) post of the good battery.
  • 4:
    Connect one end of the Negative(-) cable to the Negative(-) post of the good battery.
  • 5:
    Connect the other end of the Negative(-) cable to a good solid SHINY, NON PAINTED metal part of the engine on the dead car. Usually a giant shiny nut on the engine block will do. A painted, dirty, or oily nut will not work. You usually want to avoid placing the Negative(-) cable directly on the dead battery to minimize the chance for explosions. You should only use the ground post on the dead battery as a last resort. On this step you'll get a normal spark as you connect the ground and complete the circuit.
Why do the battery charger cables have to be connected in this order?

The reason why you connect the battery cables to the dead car battery first is because you have 3 metal cable ends dangling and potentially touching metal car parts, thus a dead battery is less likely to cause any sparking since it has little or no voltage. That is the safest starting point for your jumper cables. The 2nd battery cable clamp goes to the positive end of the good battery instead to minimize completing any circuits until we are ready to. Then the 3rd end of the battery cable goes to the ground of the good battery.

Remember, we still have not completed the circuit yet, until the 4th battery cable clamp is attached to ground. This is why this order of attaching the battery cables to your car batteries is the safest way to do it. It minimizes unnecessary sparking until the charging circuit is completed. This is good practice because excessive and unnecessary sparking could cause car batteries to fail. Since the bad battery is weak, and to prevent exploding, its ground clamp gets connected last, but not directly to the ground battery post. To prevent sparking directly on the battery, you connect the 4th battery cable clamp to a metal frame part of the dead car which is connected to the minus pole of the battery.

Many people are easily confused by this step. They cannot figure out how this completes the circuit to the battery. Car batteries have their ground cable also wired to the chassis of the car, so by clamping to a good metal chassis point, this is electrically equivalent to connecting to the ground post of your car battery.

Now, it’s time to get that battery started.

Primary method of starting the dead battery

It's critically important to shut off the boosting car’s engine while jumping the dead battery. This does, however, reduce available power to the dead car because the boosting car's alternator isn't running. The safest method is to have the good engine running a few minutes to charge the dead battery. Then shut off the good car's engine, and then disconnect the cables before starting the car that had the dead battery. If Method #1 does not work for you, try Method #2.

Secondary method of starting the dead battery

STEPS FOR Connecting the Car Battery Jumper Cables

  • 1:
    Start the good car's engine, and make sure the headlights are off to allow the maximum amount of power to get to the dead battery.
  • 2:
    Let the good car's engine run a minute or so before attempting to start the dead car. Sometimes you get lucky and the dead battery will jump-start right away, but sometimes it takes a few minutes.
  • 3:
    If there is a voltmeter built into the dash on the car with the dead battery, turn the key to the accessory setting and read the voltage coming into your charging system. Ideally you want between 12 and 13.6 volts, but some cars can start at 10 volts. If your dead car's interior dome light comes on, it's a great sign that you've connected the cables right.
  • 4:
    Now shut all doors and dome lights and try to start the car. If it sounds like it's trying to crank but won't turn over completely, give it a few more minutes and rev the engine moderately on the good car.
  • 5:
    You may also need to play with the cable grips to get a better connection, and use the in dash voltmeter to its fullest if you have one. You'll get a normal sparking as you move the cables around a bit.

Removing the jumper cables

Now that the car has been successfully jump started, you can remove the cables in the reverse order that you connected them, being careful not to let the battery cable clamps touch each other:

  • 1:
    Disconnect the Negative (-) cable from the engine block of the car that was jump-started. This breaks the circuit.
  • 4:
    Disconnect the other end of the Negative (-) cable from the Negative(-) post of the good battery.
  • 2:
    Disconnect the Positive (+) cable from the Positive (+) post of the good battery
  • 4:
    Disconnect the other end of the Positive (+) cable from the Positive (+) post of the dead battery.