How to Jump Start a Car

If you find yourself in a position where your car has broken down, or won’t start up due to a flat battery, jump starting your car is the best way to get your car going again. However, cars run on a high voltage, high enough to cause severe injury to a person if they accidentally touch a live wire, so it is essential you know how to jump start your car safely, before giving it a go.

Car breakdown on roadside with warning marker in foreground
15 Sep 2023

Equipment needed to jump start a car

To jump start a car in the UK you will need two things, a pair of working jump leads and either a battery booster pack or another vehicle with a fully-charged battery (however, you should avoid hybrid or electric cars as this can cause them damage). Your vehicle also needs to be in a spot where the jump leads can easily reach the battery.

Staying safe when using Jump Leads

While starting a car with jump leads can be easy, it can be dangerous if basic precautions are not taken. Here’s how to stay safe when jump starting a car:

Check the condition of the battery and jump leads

  • Never attempt to jump start a car battery that looks damaged or is leaking.
  • Don’t use damaged jump leads.
  • If the jump leads get hot, stop using them immediately.

Check the environment is safe

  • Before you attempt to jump start a car, remove any clothing that could get in the way, such as a scarf or tie, as these can get caught up in the moving engine parts.
  • Don’t allow any metal objects to touch the car batteries, as these could cause a spark and could even make the battery explode. Metal objects include jewellery, hand tools, stray wires, clips, etc.
  • Never smoke or allow naked flames anywhere near either battery.

Be careful when removing the jump leads

  • Once you have finished jump starting a car, don’t remove the jump leads while the car engines are running, as this can cause serious damage to the car’s electronics.

How long does jump starting a car take?

As a rule of thumb, it is good to wait about 2 minutes before you try to jump start your car to see if it starts working. However, depending on the weather, a jump start can take between 2 minutes to 30 minutes, if in extreme conditions. Following the jump start, to fully recharge the battery, you must then drive for at least 15 minutes.

Jump starting step by step

The first step to jump starting a car with leads is finding someone with a car who is happy to help. Their car must have a fully charged battery with the same voltage as yours – this is usually around 12 volts.

The step-by-step guide on how to jump start your car goes as follows:

Line up both cars together

  • Park both cars together so that their batteries are within easy reach of one another, although the cars should not touch.
  • Keep the handbrakes on and the ignitions off.

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.

Connect the black jump lead

  • Attach the black jump lead to the negative (-) terminal on the working battery.
  • Then attach the other end of the jump lead to an earthing point, well away from the flat battery and fuel system.

Start the working car

  • Keep both engines off and wait for 3 minutes. Then start up the working car’s engine and let it run for at least 1 minute.

Start your car

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

Let both cars run

  • Leave both cars running for around 10 minutes.

Turn off both cars and disconnect

  • Turn off both cars’ engines and carefully disconnect the jump leads, removing the black lead from your car first and then the red lead from the other car.
  • Make sure the leads don’t touch one another, or either car, as you remove them.

Restart your car

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

Still won’t start?

  • If your car won’t start, there may be a more serious problem requiring professional help. If you have a breakdown cover, you can call out for a professional to come assist you roadside and if needed, take you to a nearby garage so your car can be inspected.

Removing jump leads

When removing the jump leads after jump-starting your car, you must remove them in reverse order to how you attached them. The jump leads must be removed safely, so here are the steps if you’re unsure:

  • Switch off the engines on both vehicles.
  • Remove the black jump lead from the earthing point.
  • Remove the other end of the 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.

What to do when the car starts?

Once you have managed to jump start your car, the engine will need to recharge fully. To do this, drive normally (preferably not in stop-start traffic) for at least 30 minutes to charge the engine. You can also use a portable car battery charger to help top up the charge on your battery following the jump start.

How to use a battery boost pack

if you’re wondering how to jump start a car without leads, you can use a battery booster pack, which can be kept in your car for emergencies. This way, you can jump start your battery, even if you can’t get another car to help you.

The steps to jump start a car with a battery charger or battery booster pack are:

Check the battery booster pack

  • Make sure the battery pack is fully charged.
  • Place the battery booster pack somewhere stable. Don’t put it on the engine, as it can fall off when the engine starts.

Connect the red jump lead

  • Connect the red positive (+) jump lead from the battery pack to the positive (+) terminal of the car battery.

Connect the black jump lead

  • Connect the red positive (+) jump lead from the battery pack to the positive (+) terminal of the car battery.

Switch on the battery booster pack

  • Once the battery pack is connected, switch it on.

Try starting your car

  • Try starting your car by turning the key in the ignition.
  • If your car doesn’t start after a few tries, there may be a serious problem that requires help from a professional.

Success? Let the engine run

  • If the car does start, keep the engine running for at least 5 minutes.
  • After 5 minutes, switch off the battery booster pack and allow the engine to run for a further 5 to 10 minutes.

How to jump start a car in the rain

The UK is known for its unpredictable weather and unexpected showers, so it is important to know how to jump start a car in the rain. Jump starting a car in the rain is no more dangerous than doing so on a dry, sunny day, although you must make sure your jumper cables are in good condition and the insulation is not damaged.

While no immediate risk is involved with jump starting a car in the rain, doing so can expose the battery to water. This can lead to corrosion and can sometimes shorten a battery’s lifespan.

The process of jump starting a car is the same in the rain as it is in dry weather, however ultimately, you must take precautions to ensure the battery and battery do not become too wet in the process. This can be done by creating shelter, whether this is by an umbrella or a piece of clothing, which does not touch the battery.

How often should you charge your battery?

Most car batteries are not fully charged when vehicles are parked. It is suggested that you should charge your car battery once a month when the weather is warm and once every three months when the weather is colder. If you keep to this, you can extend the life of your car battery, restore the battery performance, and minimise the chances of your car breaking down. 

Top How to Jump Start FAQs:

Which jumper cable goes on first?

The red jumper cable is connected first to the working battery’s positive (+) terminal and the flat battery’s positive (+) terminal.

How long do you leave jump leads on?

Once connected, you should leave your jump leads attached to the battery for at least 3 minutes whilst the engines are off and then at least 10 minutes once the engine of the car with the flat battery has been turned on.

Can a battery be too dead to jump?

A car battery is never “too dead” to jump start. It is possible to jump start a car battery even if it is dead by following the jump start process, however, if your car still doesn’t start after this process is complete, it could be a signal of an underlying problem with your battery.

Which jump lead do I take off first?

Once the car has started, you must carefully disconnect the jump leads in reverse order. Remove the black lead first from your car and then from the other vehicle.

ASDA Money is a trading name of Asda Financial Services Ltd and Asda Stores Ltd which for Breakdown Cover are Introducer Appointed Representatives of Liverpool Victoria Insurance Company Limited.

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