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:
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"Check engine" light on – a dying battery is one possibility
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Engine cranking slowly – it's taking more time for the battery charge to reach the starter
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Dimming lights – happens when you start your car or when idling
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Corroded posts – battery acid produces terminal post corrosion, affecting the charge from the battery to the starter
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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:
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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
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Turn off cars – have both vehicles in park with the ignition turned off and the parking brake engaged
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Locate the battery – check your owner's manual for the location if you can't find it
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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
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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:
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Positive and negative – each battery has a positive (+) post — usually with a red plastic cover — and a negative (−), typically black
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Don't touch – remember not to have the jumper clamps touch once you begin attaching them to the posts
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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
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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
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Start your engines – start the car with the good battery. Wait several minutes before starting the vehicle with the dead battery
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Doesn't jump – if it doesn't turn over, check, tighten, or clean your connections; wait several minutes before starting it again
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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
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Let it charge – allow the car to run for at least 20 minutes for the battery to recharge
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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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References:
Jeff S. Bartlett, “How to Jump-Start a Car With a Dead Battery,” https://consumerreports.org/car/battery/jump-start-car-with-dead-battery-a1028630350, (Updated December 28, 2020).
“How to Jump a Car: Simple Steps to Revive Your Car Battery,” https://driving-tests.org/beginner-drivers/how-to-jump-start-a-car.
Timothy Dahl, “How to Jumpstart a Car,” https://www.popularmechanics.com/cars/a24902/how-to-jumpstart-a-car, (Published: March 27, 2020).