How to Jump Start a Car Battery

To jump start a car battery, connect jumper cables in one specific order and finish with the last black clamp on bare metal, not the dead battery. The safe sequence is: red clamp to the dead battery's positive terminal, red clamp to the good battery's positive terminal, black clamp to the good battery's negative terminal, and the final black clamp to an unpainted metal ground on the dead car, away from the battery. That last step is the one most people get wrong, and it is the one that prevents a spark from igniting the hydrogen gas a battery gives off.

An old rhyme keeps the order straight: "Red from the dead to red on the good. Black from the good, to under the hood." To disconnect: "When the battery's not dead, remove black then red."

At a glance: the four connections

Before you start: safety checks

• Do not jump a cracked, leaking, swollen or frozen battery. Jumping a damaged battery can cause it to rupture. If it looks or smells wrong, call for help.
• Check both are 12V. Almost all cars are 12V; never pair mismatched voltages.
• Park close but not touching. Position the good car within cable reach, both in park (or neutral for manual) with parking brakes on and ignitions off.
• Wear gloves and eye protection, tie back loose clothing, and no smoking near the batteries.
• For AGM, gel or lithium batteries, check the manufacturer's instructions first, as some need a specific procedure.

Step by step: jump start guide

This jump start guide assumes standard 12V lead-acid batteries and a set of jumper cables. If you have a portable jump starter, skip to the box below.

1. Position and prepare both cars. Close, not touching. Ignitions off, parking brakes on, hoods open, batteries and terminals located.
2. Red to the dead. Clamp one red end to the positive (+) terminal of the dead battery. Make sure the clamp bites onto clean metal.
3. Red to the good. Clamp the other red end to the positive (+) terminal of the good battery.
4. Black to the good. Clamp one black end to the negative (-) terminal of the good battery.
5. Black to bare metal. Clamp the final black end to an unpainted metal part of the dead car's engine or chassis, away from the battery. Do not clamp it to the dead battery's negative terminal.
6. Start the donor car, let it run a couple of minutes, then try to start the dead car.
7. If it starts, let it run and remove the cables in reverse order (black from bare metal, black from good battery, red from good, red from dead), keeping clamps from touching.
8. Drive for 20 to 30 minutes so the alternator can recharge the battery, or the car may not restart later.

Using a portable jump starter? Connect the pack's red clamp to the dead battery's positive terminal and the black clamp to unpainted metal, then follow the pack's instructions. It needs no second car, which is why it is the safer, more convenient option to keep in the boot.

If the car still will not start

A jump that fails tells you something useful. If nothing happens or you only hear a click after a good connection, either the battery is too far gone to take a surface charge, or the problem is not the battery at all. Two possibilities:

• The battery is dead beyond a jump. If it is more than 3 to 5 years old, or has needed frequent jumps lately, it likely needs replacing.
• It is the charging system. If the car starts on a jump but dies again once the cables are off, the alternator, not the battery, is probably at fault. See the alternator vs battery guide to tell them apart.

The point everyone misses: a jump is not a fix

Honest content says the uncomfortable part. Jump starting gets you moving; it does not repair anything. If the battery is worn out, it will strand you again, often the very next morning. If a light left on or a short drive drained a healthy battery, a good drive will recharge it and you are fine. But if the battery is old or keeps dying, treat the jump as a lift to the shop, not a repair. A dead car battery that repeatedly needs jumping is telling you it is time for a new one.

Honest limits and cautions

What a jump start handles well: a healthy battery flattened by an accidental drain. What it does not: a failed battery, a failed alternator, or a deeper electrical fault. Reversing the clamps (red to negative) can damage the battery and fry sensitive electronics, so double-check polarity. Modern cars packed with electronics are less tolerant of mistakes, so when in doubt, use a portable jump starter with built-in reverse-polarity protection, or call roadside assistance.

Who this is for

• Every driver: know the order and keep jumper cables or a jump starter in the car.
• Owners of older cars: most likely to face a dead battery; a jump starter pays for itself in one roadside save.
• EV owners: your car's small 12V battery can be jumped like any other, but never attempt anything with the high-voltage traction pack (see the EV vs car battery guide).

Conclusion

To jump start a car battery safely, follow the order (red to dead, red to good, black to good, black to bare metal) and never clamp the final black lead to the dead battery itself. Check both batteries are sound and 12V, drive for 20 to 30 minutes afterwards, and remember that a jump is a lift, not a repair. If a dead car battery keeps needing jumps, replace it; if the car dies again once the cables are off, suspect the alternator. Keep a portable jump starter in the boot as the simplest, safest fix, and when the old battery is done, dispose of it responsibly.

FAQs

What is the correct order to jump start a car battery?
Red clamp to the dead battery's positive terminal, red clamp to the good battery's positive terminal, black clamp to the good battery's negative terminal, and the final black clamp to unpainted metal on the dead car, away from the battery. Remove in reverse order.

Why does the last black clamp go on metal, not the battery?
Because a battery gives off hydrogen gas, and the final connection can spark. Clamping to bare metal away from the battery keeps that spark away from the gas, reducing the risk of ignition. It also gives a solid ground for the circuit.

How long should I drive after jumping a dead car battery?
Drive for at least 20 to 30 minutes so the alternator can recharge the battery. If you switch off too soon, the battery may not have enough charge to restart the car, and you could be stranded again.

Can I jump start a car alone with a portable jump starter?
Yes. A portable jump starter needs no second car: connect its red clamp to the dead battery's positive terminal and the black clamp to bare metal, then follow its instructions. Built-in reverse-polarity protection makes it the safest option to keep in the car.

What if the car will not start even after a jump?
Either the battery is too far gone or the fault is elsewhere. If the car starts on a jump but dies once the cables come off, suspect the alternator. If it will not take a charge at all and is over three to five years old, the battery likely needs replacing.

Is it safe to jump start a car in the rain?
Yes. A 12V car battery's voltage is too low to make rain a shock hazard for this task, so jumping in the rain is safe. Still follow the correct clamp order and keep the clamps from touching each other.

Can I damage my car by connecting jumper cables wrong?
Yes. Reversing polarity (red to negative) can damage both batteries and fry sensitive electronics like the engine computer. Always match red to positive and black to negative or ground, and double-check before you start either car.

Does jump starting fix a dead battery?
No. A jump start gets the engine running but repairs nothing. A healthy battery drained by accident will recharge as you drive, but a worn-out battery will die again. If a battery keeps needing jumps, replace it rather than relying on repeated jumps.