Jump starting a car means using another vehicle's battery to restart yours
A jump start transfers electrical power from a working battery to a dead one through jumper cables. You connect the cables in a specific order, start the working vehicle first, then start yours. The process takes about five minutes, and the working car's alternator recharges your battery as both vehicles run. If you follow the steps in the wrong order, you risk damaging both batteries or getting shocked.
You will need jumper cables (the red and black wires with clamps on each end), another vehicle with a working battery, and both drivers present. The cars should be parked close enough that the cables reach between them, but not touching. If your battery is cracked, leaking, or visibly damaged, do not attempt a jump start — call a tow truck instead.
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 engine block — not the negative terminal of the dead battery.
- Start the working vehicle and let it run for two to three minutes before starting yours.
- 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 for at least twenty minutes after a successful jump start so the alternator can recharge your battery.
Locate both battery terminals before you connect anything
Open the hood of both vehicles and find the battery. On most cars it sits in the engine bay on one side. The battery has two terminals — the positive terminal is marked with a plus sign (+) and usually has a red plastic cover. The negative terminal is marked with a minus sign (−) and is usually black or bare metal.
If either battery has a plastic cover over the terminals, remove it by hand or with a wrench. Look at the battery case itself. If you see cracks, white or blue powder around the terminals, or liquid leaking, do not proceed. A damaged battery can explode or leak acid when you connect cables to it.
Connect the red cable to both positive terminals in order
Take the red jumper cable. Clamp one end firmly onto the positive terminal of the dead battery — the one with the plus sign. You should hear or feel a click as the clamp seats. Tighten the clamp by hand if it has a screw.
Walk to the working vehicle and clamp the other end of the red cable to its positive terminal. Again, make sure the connection is tight. At this point you have a complete circuit between the two batteries, but no current is flowing yet because the working vehicle is off.
Connect the black cable to the working battery and engine block
Take the black jumper cable. Clamp one end to the negative terminal of the working battery only. This is the critical step that most people get wrong. Do not clamp the black cable to the negative terminal of the dead battery.
Instead, take the other end of the black cable and clamp it to an unpainted metal surface on your engine block — a bolt, a bracket, or the engine itself. This grounds the circuit and prevents sparks near the dead battery, which could ignite hydrogen gas that accumulates inside old batteries. The metal surface must be bare; paint acts as an insulator.
Start the working vehicle and wait before starting yours
Get into the working vehicle and start the engine. Let it run for two to three minutes. During this time, the alternator in the working vehicle is pushing current through the cables into your dead battery, slowly bringing it back to life.
After two to three minutes, try to start your vehicle. If it does not turn over, wait another minute and try again. If it still will not start after three attempts, stop and call a tow truck. Repeated attempts can overheat the starter motor and cause additional damage.
Remove the cables in reverse order to avoid sparks
Once your vehicle is running, remove the cables in the exact reverse order you connected them. This prevents a spark that could damage the alternator or battery.
First, remove the black cable from your engine block. Second, remove the black cable from the working vehicle's negative terminal. Third, remove the red cable from the working vehicle's positive terminal. Fourth and last, remove the red cable from your positive terminal. Coil the cables and set them aside.
Drive for at least twenty minutes to recharge the battery
Keep your engine running and drive for at least twenty minutes. The alternator recharges the battery while the engine runs. If you turn off the engine when ready after the jump start, the battery may not have enough charge to start the car again.
If the car dies again within a few days, the battery itself is likely dead and needs replacement. A jump start is a temporary fix; it does not repair a failing battery. If the car starts and runs normally, the battery may have been drained by leaving lights on or by a parasitic drain, and the jump start was sufficient.
What to do if the jump start does not work
If the engine does not turn over after waiting and trying again, the problem may not be the battery. A dead alternator, a bad starter motor, or a fuel system failure can prevent starting even with a working battery. In this case, call a tow truck rather than attempting multiple jump starts.
If you smell rotten eggs or see smoke coming from the battery, stop when ready and move away from the vehicle. These are signs of a chemical reaction inside the battery. Do not attempt another jump start and do not touch the battery. Call emergency services if smoke is heavy.
Frequently Asked Questions
Can I jump start a car if the battery is completely dead?
Yes. A completely dead battery has no charge, but it can still accept and hold a charge from another battery. The jump start process works the same way. If the battery is cracked or leaking, however, do not attempt it.
What if I connect the cables in the wrong order?
If you connect the black cable to the negative terminal of the dead battery instead of the engine block, you risk a spark near the battery. If you connect the red cable to the negative terminal by mistake, you will short-circuit the batteries and may damage both vehicles' electrical systems. Disconnect when ready and start over if you realize you made an error.
How long does a jump start take?
The actual process takes about five minutes: two to three minutes of the working vehicle running, then one to two minutes to start your car and remove the cables. After that, you need to drive for at least twenty minutes to recharge the battery fully.
Do I need to turn off both vehicles before removing the cables?
No. Remove the cables while both vehicles are running. Turning off the working vehicle before you disconnect can cause a voltage spike that damages electronics in both cars.
What if the jumper cables are too short to reach between the vehicles?
Park the vehicles closer together so the cables can reach. The cars should not touch, but the cables must reach from one battery to the other without stretching. If you cannot get close enough, you need a tow truck or a longer set of cables.