Safety Center

How To Jump-Start a Car Safely

A car battery typically lasts three-to-five years, depending on your area's climate, although some batteries can last up to seven years. Be prepared for a dead battery by having jumper cables in your trunk.

Signs your battery may be going bad, and you should take your vehicle to a mechanic:

  • "Check engine" light on – a dying battery is one possibility

  • Engine cranking slowly – it's taking more time for the battery charge to reach the starter

  • Dimming lights – happens when you start your car or when idling

  • Corroded posts – battery acid produces terminal post corrosion, affecting the charge from the battery to the starter

  • Battery drain – a bad alternator, broken fuse, or accidentally left on interior lights or headlights could slowly drain the battery

Before you begin the jump-start:

  • Get close – safely park the "good" car next to the vehicle with the dead battery; ideally 18 inches away, to enable the jumper cables to reach

  • Turn off cars – have both vehicles in park with the ignition turned off and the parking brake engaged

  • Locate the battery – check your owner's manual for the location if you can't find it

  • Check posts – clean off any powdery corrosion on the posts of either car with a brush or cloth, and avoid touching or inhaling the corrosion dust

  • Inspect jumper cables – look for any cracks in the clamps or exposed wires in the cables; don't use them if you see any wear and tear

Beginning the jump-start:

  • Positive and negative – each battery has a positive (+) post — usually with a red plastic cover — and a negative (−), typically black

  • Don't touch – remember not to have the jumper clamps touch once you begin attaching them to the posts

  • Positive to positive – securely clamp one end of the positive (red) cable to the dead battery's positive post (red cap); take the red clamp on the other cable and attach it to the positive post of the car with the working battery

  • Negative to negative – attach the black clamp of the cable on the working battery and connect to the negative post; firmly attach the remaining black clap to a non-painted metal surface (such as a bracket or bolt) to ground it on the main block of the dead battery vehicle

  • Start your engines – start the car with the good battery. Wait several minutes before starting the vehicle with the dead battery

  • Doesn't jump – if it doesn't turn over, check, tighten, or clean your connections; wait several minutes before starting it again

  • Jump is successful – if your engine turns over, carefully remove the jumper cables in reverse order — black from engine metal, black from the good car, red from the good car, and black from the formerly dead battery

  • Let it charge – allow the car to run for at least 20 minutes for the battery to recharge

  • Time to call for help – if your car doesn't start, remove the cables in reverse order (see above) and call for roadside assistance

Contact a professional for assistance if you are not comfortable performing any of these steps. You may need another jump-start if the battery or alternator is not functioning correctly. Take it to your mechanic if that happens.

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  1. Jeff S. Bartlett, “How to Jump-Start a Car With a Dead Battery,”, (Updated December 28, 2020).

  2. “How to Jump a Car: Simple Steps to Revive Your Car Battery,”

  3. Timothy Dahl, “How to Jumpstart a Car,”, (Published: March 27, 2020).

Our Safety Center pages are filled with tips related to the safety and maintenance of your home and autos. The information contained in these articles should not be construed as professional advice, and is not intended to replace official sources. Other resources linked from these pages are maintained by independent providers; therefore, NJM cannot guarantee their accuracy.