How to Jump Start a Car: Jump Leads Order and Safety Steps

A flat battery is one of the most common reasons a car won't start, especially after a cold night or a few weeks parked up. With a set of jump leads and a second car, you can often get going again in a few minutes. Done in the wrong order, though, jump starting can cause sparks, damage the car's electronics or injure you.

I've based every step here on the AA's own jump start guide. The AA says it would prefer drivers call a breakdown service and let a trained mechanic do it, and that your car's handbook comes first wherever it differs from the general steps. Where the battery sits and where the leads should go can vary between makes, so check the handbook before you clip anything on.

What you need to jump start a car

• A pair of working jump leads, one red and one black.
• Rubber work gloves.
• A donor car with a fully charged battery of the same voltage, which the AA says is usually 12 volts.
• Space to park the two cars close enough for the leads to reach both batteries.

The AA says not to use a hybrid or electric car as the donor vehicle. If your own car is a hybrid or electric model, follow its handbook rather than general advice.

Jump start safety checks before you begin

• Don't jump start a battery that looks damaged or is leaking.
• Don't use damaged leads, and stop if the leads get hot.
• Take off scarves, ties or anything dangling that could catch in moving engine parts.
• Remove metal jewellery and watches, and keep metal tools away from the battery terminals. The AA warns that metal can cause sparks and battery explosion.
• Keep cigarettes and naked flames well away from both batteries.
• If it's raining, keep the engine bay as dry as you can. The AA says it's possible but not ideal.

Connecting jump leads in the right order

Park the cars close together without them touching. Put both handbrakes on and switch both ignitions off. Then connect the leads in this order:

1. Clip one end of the red lead to the positive (+) terminal on the donor car's battery.
2. Clip the other end of the red lead to the positive (+) terminal on the flat battery.
3. Clip one end of the black lead to the negative (-) terminal on the donor car's battery.
4. Clip the other end of the black lead to an earth point on the car with the flat battery. The AA describes this as unpainted metal on the engine block or chassis, well away from the battery and the fuel system.

Never let the red and black clips touch each other while any of them are connected. If your car has a stop-start battery, the AA says jump starting is fine, but use an earth point on the engine or chassis rather than the negative terminal.

Starting the car with the flat battery

1. With both engines off, wait 3 minutes.
2. Start the donor car and let it run for 1 minute.
3. Start the car with the flat battery.
4. Let both cars idle at a fast pace for around 10 minutes.

If the car won't start after a few tries, stop. The AA says there's probably a more serious problem, and it's time to call for help.

Removing jump leads safely

Switch both engines off before you take anything off. The AA warns that removing leads while the engines are running can seriously damage the cars' electronics. Then remove the leads in reverse order:

1. Black lead from the earth point on the car that was flat.
2. Black lead from the donor battery's negative terminal.
3. Red lead from the donor battery's positive terminal.
4. Red lead from the positive terminal of the battery that was flat.

Keep the clips from touching each other or either car as you take them off.

After the car starts: recharging the battery

Once the leads are off, try starting the car again. If it starts, the AA suggests driving normally for at least 30 minutes, avoiding stop-start traffic, to put charge back into the battery. A portable charger can also top it up.

If the battery keeps going flat, it may be near the end of its life. The AA says batteries last 5 to 7 years on average, and it's worth having a battery over 5 years old checked if it's struggling to start the car.

Using a jump starter pack instead of leads

A battery booster pack, sometimes called a jump starter, means you don't need a second car. The AA's steps are:

1. Check the pack's fully charged and place it somewhere stable, not on the engine.
2. Connect the red (+) lead from the pack to the battery's positive (+) terminal.
3. Connect the black (-) lead to an earth point, such as unpainted metal on the engine block or chassis.
4. Switch the pack on and try to start the car.
5. If it starts, let the engine run for about 5 minutes, then switch off the pack and let the engine run for a further 5 to 10 minutes.
6. Turn the engine off, remove the black lead first and the red lead second, then try starting again.

If the car won't start after a few attempts with a pack either, call for professional help.

When to call a breakdown service instead

• The battery is cracked, leaking or damaged.
• You don't feel confident doing it yourself.
• The car still won't start after jump starting or using a booster pack.

AA members can also have their battery tested, and the AA says its Battery Assist team can replace a dead battery on the same day. And if a warning symbol stays on once you're running, it's worth knowing what the check engine light means before you set off.

Sharing your motoring know-how

If you're a mechanic or simply love explaining how cars work, guides like this one are always in demand with drivers.

Write about cars? Here's where to send it: motoring blogs that take outside articles.

Frequently asked questions

What order do you connect jump leads?

The AA's order is red to the donor battery's positive, red to the flat battery's positive, black to the donor battery's negative, then black to an earth point on the car with the flat battery, such as unpainted metal on the engine block.

Which order do you remove jump leads?

Switch both engines off first, then remove them in reverse: black from the earth point, black from the donor battery, red from the donor battery, then red from the battery that was flat.

How long should I run the car after a jump start?

The AA suggests driving normally for at least 30 minutes, avoiding stop-start traffic, to recharge the battery.

Can a hybrid or electric car be used to jump start another car?

The AA says not to use a hybrid or electric car as the donor. If your own car is a hybrid or electric model, follow its handbook.

Why won't my car start after a jump start?

If it won't start after a few attempts, the AA says there's probably a more serious problem. Call a breakdown service rather than keep trying.