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How to jump start a car

Feeling flat? Here's how to use jump leads

A jump start is a handy way to start a car with a flat battery. But jump leads can cause damage to both cars and people if they’re not used properly.

For your safety, and our peace of mind, we’d always prefer you to give us a call and leave the jump starting to our trained mechanics.

Broken down?

Call us on 0800 88 77 66 or request help via the AA app

If you’re keen to do it yourself, take a look at our advice on how to jump start a car. But make sure you read the instructions in your handbook and follow those if they're different to our steps.

In this article:

Using jump leads

What you'll need to jump start a car

  • A pair of working jump leads (you can buy ours here).
  • The vehicle with the flat battery, which needs to be in a spot where jump leads can easily reach the battery.
  • Another vehicle with a fully-charged battery (avoid a hybrid or electric car as this could cause damage).
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Using jump leads safely

Before you try to jump start a car, remember that batteries produce flammable gases. Here's how to stay safe:

Check the battery and jump leads
  • Never try to jump start a battery that looks damaged or is leaking.
  • Don’t use jump leads that are damaged.
  • Stop using the jump leads if they get hot.
Make sure the environment is safe
  • Before you start, remove any dangling clothing – like a scarf or tie – as it could get caught up in the moving engine parts.
  • Don’t let any metal objects touch the car batteries - these could cause a spark and possibly make the battery explode. That includes rings, necklaces, watch straps, hand tools, clips, stray wires etc.
  • Never smoke or allow naked flames anywhere near either battery.
Take care removing the jump leads
  • Don't remove the jump leads while the car engines are running. This can cause serious damage to the cars’ electronics.
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A step-by-step guide to jump starting a car

Find someone with a car who’s happy to help. Their car must have a fully charged battery with the same voltage as yours (usually 12 volts).

1. Line up both cars

  • Park both cars so their batteries are within easy reach of one another (without the cars actually touching).
  • Keep the handbrakes on and the ignitions off.

2. Connect the red jump lead

  • Use the red jump lead to connect the working battery’s positive (+) terminal to the flat battery’s positive (+) terminal.

3. Connect the black jump lead

  • Take the black jump lead and attach it to the negative (-) terminal on the working battery.
  • Then attach the other end to an earthing point (unpainted metal on the engine block or chassis) well away from the flat battery and fuel system.

4. Start the other car

  • Keep both engines off and wait for 3 minutes, then start the working car’s engine and let it run for 1 minute.

5. Start your car

  • Turn on the engine in the car with a flat battery.

6. Let both cars run

  • Leave both cars to idle, at a fast pace, for around 10 minutes.

7. Turn off and disconnect

  • Turn off both cars’ engines and carefully disconnect the leads in the reverse order to the way they were connected (remove the black lead from your car first and finish with the red lead from the other car).
  • Make sure the leads don’t touch one another, or either car, as you remove them.

8. Restart your car

  • Try turning the keys in the ignition to see if your car will start up.

9. Call for help

  • If your car won’t start there’s probably a more serious problem requiring professional help.
  • If you’re still stuck, you can call us on 0800 88 77 66 or by using the AA app.
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How to remove the jump leads

You remove the jump leads in the reverse order to how you attached them. But if you're not sure, here are the steps:

  • Switch off the engines on both vehicles.
  • Take the black jump lead off the earthing point.
  • Remove the other end of the black jump lead from the working battery's negative (-) terminal.
  • Disconnect the red jump lead from the working battery's positive (+) terminal.
  • Remove the other end of the red jump lead from the positive (+) terminal on the flat battery.
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How to jump start a car with a battery booster pack

It can be a good idea to keep a car battery booster pack in your car. That way, you can jump start your battery even if you can’t get another car to help you.

Before you start, make sure:

  • The car battery doesn’t look damaged and isn’t leaking.
  • You’ve taken off any metal jewellery or watches and removed dangling clothing like a tie or scarf.

Steps to using a car battery booster

1. Check the battery booster
  • Make sure the pack's fully charged
  • Put the battery booster pack somewhere stable. Don’t put it on the engine as it might fall off when the engine starts.
2. Connect the red jump lead
  • Connect the red positive (+) jump lead from the battery pack to the positive (+) terminal of the car battery.
3. Connect the black jump lead
  • Connect the black negative (-) jump lead to an earthing point on your car. Unpainted metal on the engine block or chassis is best.
4. Switch on the pack
  • Once the battery pack's connected, switch on the pack.
5. Try to start the car
  • Try to start your car by turning the key in the ignition.
  • If it doesn’t start after a few tries, there’s probably a more serious problem that needs professional help. If you’re still stuck, you can call us on 0800 88 77 66 or use the AA app.
6. Let the engine run
  • If the car starts, keep the engine running for about 5 minutes.
  • After 5 minutes, switch off the boost pack and allow the engine to run for a further 5 to 10 minutes.
7. Turn off and disconnect
  • Turn off the engine.
  • Remove the leads in the reverse order to how you placed them on (first disconnect the black lead, then the red lead).
8. Restart your car
  • Try turning the keys in the ignition to see if the car starts up again.
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What to do after you’ve jump started your car

If you’ve managed to jump start your car, the engine will need to recharge again fully.

Charge the engine by driving normally (not in stop-start traffic) for at least 30 minutes. You can also use a portable car battery charger to top up the charge on your battery.

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How often should you change a car battery?

On average, batteries last between 5 and 7 years but you should only consider changing a car battery when it's showing signs of deterioration.

If the battery's more than 5 years old and seems like it's struggling to start the car, get it checked out. It's better to be safe than sorry - it'll be worse if it's a roadside emergency or on a cold morning when you're already late for work.

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Published: 21 August 2017 | Updated: 5 February 2020 | Author: The AA

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