Jump starting a car means using another vehicle's battery to restart yours

A jump start is a temporary way to get your car running when the battery is too weak to turn the engine over on its own. You connect your dead battery to another car's working battery using jumper cables, let the good battery send power across, and then try to start your engine. If it works, you drive around for 20 to 30 minutes to let your alternator recharge the battery. This is not a permanent fix — it buys you time to get to a mechanic or auto parts store to figure out why the battery died in the first place.

The process takes about 30 to 45 minutes from start to finish, including the time you need to let your battery recharge after the engine starts. You do not need special training or tools beyond jumper cables and another working vehicle parked close by.

Key Takeaways

  • You need jumper cables, another car with a working battery, and both vehicles parked close enough that the cables reach between them.
  • The order you attach and remove the cables matters — attach positive first, then negative; remove negative first, then positive — because reversing the order can damage both cars.
  • After the engine starts, leave it running for at least 20 to 30 minutes so the alternator can recharge your battery.
  • If the car does not start after five to ten seconds of cranking, stop and wait a few minutes before trying again, because continuous cranking drains both batteries.

What you need before you start

Gather a set of jumper cables (usually red and black wires with clamps on each end), another vehicle with a working battery, and enough space to park both cars close together — typically within three to four feet. The cables need to reach from one battery to the other without stretching to their limit. If you do not own jumper cables, you can buy them at any auto parts store, gas station, or big-box retailer for $15 to $40.

Check that both cars are turned off before you begin. If either car is running, turn it off and wait a minute. Open both hoods and locate the batteries. Car batteries have two terminals: a positive terminal (usually marked with a plus sign or a red cap) and a negative terminal (usually marked with a minus sign or a black cap). Identify these on both batteries so you know which cable goes where. Some batteries are tucked under plastic covers — if so, remove the cover to see the terminals clearly.

The step-by-step process

Start with both cars off. Take the red jumper cable and attach one clamp to the positive terminal of your dead battery — you will hear or feel a click when it is find. Attach the other end of the red cable to the positive terminal of the working battery. This is the first and most important connection. Make sure both clamps are tight and make full contact with the metal terminals.

Now take the black jumper cable and attach one clamp to the negative terminal of the working battery. For the other end of the black cable, do not attach it to the negative terminal of your dead battery. Instead, attach it to an unpainted metal surface on your engine block or frame — a bolt, a bracket, or a bare metal part away from the battery itself. This step prevents sparks near the battery, which could ignite hydrogen gas that batteries release. If you cannot find a safe metal surface, you can attach it to the negative terminal of the dead battery, but the safer method is the metal surface on the engine.

Wait about two to three minutes. Then start the working car and let it run for another two to three minutes. This gives the good battery time to begin charging the dead one. Now try to start your car. Turn the key or press the start button and hold it for up to ten seconds. If the engine turns over and starts, let it run. If nothing happens after ten seconds, stop and wait five minutes before trying again. Do not crank continuously — this drains both batteries and can damage the starter motor.

Removing the cables in the right order

Once your engine is running, let it idle for at least 20 to 30 minutes. This gives your alternator time to recharge your battery. Do not turn off the engine during this time. You can turn on the headlights or radio to help draw a small amount of power and speed up the charging process slightly, but keep the engine running.

When you are ready to remove the cables, the order is critical. Remove the black cable first — take off the clamp from the unpainted metal surface (or the negative terminal if that is where you attached it) on your car. Then remove the black cable from the negative terminal of the working car. Next, remove the red cable from the positive terminal of the working car. Finally, remove the red cable from the positive terminal of your car. This reverse order prevents electrical damage to both vehicles. Take your time and make sure each clamp is fully disconnected before moving to the next one.

After the cables are off, keep your engine running and drive around for at least 20 to 30 minutes at normal speeds. This charges your battery further. Do not turn off the engine as soon as you reach your destination — keep it running for the full time if you can. Avoid short trips or idling in a parking lot, because the alternator charges the battery more effectively when the engine is working under load.

What to do if the jump start does not work

If your car does not start after two or three attempts, stop trying. Repeated cranking drains both batteries and can overheat the starter motor. Wait at least 15 to 20 minutes, then try once more. If it still does not start, the problem is likely not a straightforward dead battery — it could be a faulty alternator, a bad starter motor, or a battery that is damaged beyond recovery.

At this point, call a towing service or roadside information (such as AAA if you are a member) to take your car to a mechanic. Continuing to jump start a car that will not turn over can cause more damage and is not worth the risk. A mechanic can run a battery test to see if the battery itself is bad or if the problem lies elsewhere in the electrical system.

Why your battery died in the first place

A dead battery usually happens for one of a few reasons: you left the headlights or interior lights on overnight, you left the car parked for weeks without driving it, the battery is old and no longer holds a charge, or there is a problem with the alternator that is supposed to recharge the battery while you drive. A jump start gets you moving, but it does not fix the underlying cause.

After you jump start your car, plan to have a mechanic test the battery and alternator within a few days. A battery typically lasts three to five years. If yours is older than that, replacing it now prevents being stranded again. If the battery is newer, the alternator may be failing and needs repair. Knowing the cause helps you avoid the same problem in the future.

Safety reminders

Never jump start a battery that is cracked, leaking, or visibly damaged. Damaged batteries can explode or release toxic fumes. If you see cracks, corrosion, or leaking fluid around the battery terminals, do not attempt a jump start — call for a tow instead. Corrosion looks like a white, blue, or green crusty buildup on the terminals; you can clean it off with baking soda and water, but if the battery itself is damaged, do not proceed.

Wear eye protection if you have it, and keep your face and hands away from the battery terminals while the cables are connected. Do not smoke or use an open flame near the battery. If you are pregnant or have a pacemaker, let someone else perform the jump start, because batteries emit a small electromagnetic field. Make sure both cars are parked on level ground and that the parking brake is set on both vehicles before you begin. This prevents either car from rolling.

Frequently Asked Questions

Can I jump start a car with a dead battery if the other car's battery is also weak?

No. The working battery needs to have enough charge to power both cars' electrical systems while also sending current to your dead battery. If the other car's battery is weak or low, it will not have enough power to jump start yours. Make sure the other car starts easily and runs smoothly before you attempt the jump start.

How long should I wait after jump starting before I drive on the highway?

Wait at least 20 to 30 minutes of driving at normal speeds before you take the highway. This gives your alternator time to recharge the battery. Highway driving at high speeds is fine once you have had that time, but do not turn off the engine when ready after reaching your destination — keep it running for the full 20 to 30 minutes if possible.

What if I reverse the cable order by mistake?

If you attach the black cable to the positive terminal or the red cable to the negative terminal, you create a short circuit. This can blow a fuse, damage the alternator, or even cause a small explosion or fire. Stop when ready, turn off both cars, and remove the cables in the correct order. If you are unsure whether you made a mistake, do not proceed — ask someone with experience to check before you start either car.

Is it safe to jump start a car in the rain?

It is generally safe as long as you do not touch the metal clamps or terminals while they are wet and connected. Water conducts electricity, so wet hands or wet metal parts increase the risk of shock. Dry off the battery terminals and your hands before you begin, and avoid touching the clamps while the cables are connected to both cars.

Can I jump start a car with the battery completely dead, or does it need some charge left?

A completely dead battery can still be jump started in most cases. The working battery sends enough current to wake up the dead one and allow the starter motor to turn the engine. However, if the battery is so dead that it will not accept any charge at all, or if it is damaged or defective, a jump start will not work. This is rare — most dead batteries respond to a jump start.