Jump starting a car requires two vehicles, jumper cables, and about ten minutes
A jump start uses another car's battery to give your dead battery enough power to turn the engine over. You connect the two batteries with jumper cables in a specific order, let the working car run for a few minutes, then start your car. The process is safe if you follow the steps in order — the order matters because it controls where the electrical current flows and prevents sparks near the battery terminals.
You will need a second vehicle with a working battery, a set of jumper cables (usually 10 to 20 feet long), and both cars parked close enough that the cables reach from one engine bay to the other. If you do not have jumper cables, you can buy them at any auto parts store or gas station for $15 to $40. If you do not have access to another car, you will need to call a towing service or roadside information.
Key Takeaways
- Connect the red cable to the positive terminal of the dead battery first, then to the positive terminal of the working battery.
- Connect the black cable to the negative terminal of the working battery, then to an unpainted metal surface on your car's engine — not the negative terminal of the dead battery.
- Let the working car run for two to three minutes before starting your car.
- Remove the cables in reverse order: black from your car, black from the working car, red from the working car, red from your car.
- Drive your car for at least 20 minutes after a successful start so the alternator can recharge the battery.
Locate both battery terminals and position the cars
Open the hood of both vehicles and locate the battery in each engine bay. The battery is a rectangular plastic box with two metal terminals on top — one marked with a plus sign (+) for positive and one marked with a minus sign (−) for negative. The positive terminal is usually red or has a red plastic cover; the negative terminal is usually black or has a black plastic cover.
Park the working car close enough to your car so the jumper cables can reach from one battery to the other without stretching tight. You do not need the cars touching, but they should be within 3 to 4 feet. Turn off both engines and make sure both cars are in Park (or Neutral if manual transmission) with the parking brake set.
If either battery terminal is corroded (covered in white, blue, or green crusty buildup), use a wire brush or old toothbrush to scrub it clean before connecting the cables. Corrosion blocks the electrical connection and can prevent the jump start from working.
Connect the red cable to both positive terminals
Take the red jumper cable and attach one end to the positive terminal of your dead battery. Push the clamp firmly onto the terminal until it clicks or grips tightly. The connection should be solid enough that you cannot wiggle the clamp by hand.
Take the other end of the red cable and attach it to the positive terminal of the working battery in the same way. You have now created a path for positive current from the working battery to your dead battery. Do not let the other end of the red cable touch any metal on either car while you are making this connection.
Connect the black cable to the working battery and your engine
Take the black jumper cable and attach one end to the negative terminal of the working battery. Push the clamp on firmly, the same way you did with the red cable.
Take the other end of the black cable and attach it to an unpainted metal surface on your car's engine — not to the negative terminal of your dead battery. Look for a bolt, bracket, or bare metal surface on the engine block or frame. This step is important: connecting to an unpainted metal surface instead of the negative terminal reduces the risk of a spark near the battery, where hydrogen gas may be present.
Start the working car and wait before starting yours
Start the engine of the car with the working battery and let it run for two to three minutes. This gives the working alternator time to charge your dead battery enough to turn your engine over. You will see the engine idle normally — there is no need to rev it or press the gas pedal.
After two to three minutes, try to start your car. Turn the key or press the start button as you normally would. If the engine turns over and starts, move to the next step. If nothing happens or the engine cranks but does not start, wait another minute and try again. If your car still will not start after three attempts, the battery may be too dead or there may be another problem — stop trying and call for roadside information.
Remove the cables in reverse order
Once your car is running, remove the jumper cables in the exact reverse order you connected them. This order prevents electrical surges that could damage either car's electrical system.
First, remove the black cable from your car's engine. Unclamp it and set it aside. Second, remove the black cable from the working car's negative terminal. Third, remove the red cable from the working car's positive terminal. Fourth and last, remove the red cable from your car's positive terminal. Coil the cables and set them aside.
Keep both cars running. Do not turn off your car when ready after the jump start.
Drive your car to recharge the battery
Let your car idle for a minute or two, then drive it for at least 20 to 30 minutes at normal highway or city speeds. The alternator (a component that generates electricity when the engine runs) will recharge the battery during this time. Avoid stopping and starting repeatedly, and do not turn off the engine until you have driven for the full time.
If your car dies again after you turn it off, the battery is likely damaged and needs to be replaced. If it starts again the next time you try, the jump start worked and the battery has recovered enough charge to hold. Either way, have the battery tested at an auto parts store or mechanic within a few days — the test is usually free, and a battery that needed a jump start may be nearing the end of its life.
Frequently Asked Questions
What if I connect the cables in the wrong order?
If you connect the black cable to the negative terminal of your dead battery instead of to an unpainted metal surface on your engine, you risk a spark near the battery. This is dangerous if hydrogen gas is present. If you realize the mistake before starting the working car, disconnect and reconnect correctly. If you have already started the working car, disconnect the cables in reverse order and start over.
Can I jump start a car with a dead battery if the battery is cracked or leaking?
No. A cracked or leaking battery is unsafe to jump start because the acid inside can splash or the battery can fail suddenly during the process. If the battery case is damaged, call for a tow instead. A mechanic or roadside service can replace the battery or tow your car to a repair shop.
How long should I let the working car run before I try to start mine?
Two to three minutes is usually enough. If your battery is very dead, you may need to wait longer — up to five minutes. There is no harm in waiting longer, but there is a risk in trying to start too soon. If your car does not start after two to three minutes, wait another minute and try again.
Do I need to turn off the working car before I remove the cables?
No. Keep the working car running while you remove the cables. Removing the cables while both cars are running is safer than turning off the working car first, because it prevents electrical surges. Once all cables are off, you can turn off the working car if you want, but your car should stay running for at least 20 minutes.
What if my car still will not start after a jump start?
The battery may be too damaged to hold a charge, or there may be another problem with the car's electrical or starting system. Stop trying after three attempts — repeated cranking drains the working battery and can damage your starter motor. Call roadside information or a towing service to have your car inspected by a mechanic.