How to jump start your car

Leaving your car’s lights on overnight. Freezing temperatures. Or an old or poorly maintained battery. All these can quickly lead to an engine that fails to start.

But a flat battery doesn’t have to ruin your day. With jumper cables and equipment, you can jump start your car from another vehicle’s battery or a battery pack and get on your way.

EASY AS HACK

Use high-quality thick jump leads to improve your chances of a successful jump start. Lightweight cables may be cheaper, but they can’t take the load needed to jump start a car battery. As for length, a 5-metre cable should be long in most situations.

What you need to jump start your car

Before you begin, gather all the equipment you need to jump start the car:

• Black negative (-) and red positive (+) jump leads with insulated terminal clamps
• A second donor car with a charged battery (or a portable battery pack)
• Thick gloves and goggles for safety
  
  

Safety advice before jump starting a car

Incorrect use of jump leads and batteries could damage the car’s electrical system or cause injuries such as burns and shocks, so be careful. If you’re unsure, then it’s best to get in touch with a reputable mechanic or garage who can help.

• Check that the battery isn’t leaking or damaged, as the acid in a battery can burn the skin. If you’re not confident, do not begin the jump start. Get advice from a professional, such as a breakdown service¹
• Choose good quality jump leads, as they could improve your chances of jump starting a car.
• Never work by naked flames or close to someone who is smoking - keep them far away from the battery. The risk of an explosion is genuine if a spark ignites the hydrogen gas generated inside a car’s lead-acid battery²
• Remove jewellery¹ like wristwatches, rings and bracelets, as metal items are electrical conductors that could heat up and cause burns or shock. Another potential hazard is a spark and explosion if the metal touches the battery terminals.
• Check your vehicle’s manual before you begin, as there could be specific instructions or precautions you need to take.³
• Take the key out of the ignition¹

Step-by-step guide to jump starting a car

1. Switch off any electrical systems or devices

Before you try to jump start a car, the first step is to make sure all electrical items in the donor car, such as the radio, sat-nav and headlamps, are off. You want to prevent power surges.

2. Locate the vehicle battery

Put on protective gloves⁴ and safety goggles before opening the bonnet. The battery is usually found under the bonnet, although in some vehicles it may be in the boot.⁵ Even if the battery is elsewhere, you may still find jump-start connection points under the bonnet. If you're unsure where to find them, check your vehicle handbook.

Before connecting the jump leads, make sure both vehicles use the same battery voltage. Most cars use a 12-volt battery. Never attempt to jump start a vehicle using a hybrid or electric vehicle battery.¹

Next, identify the positive (+) and negative (-) terminals¹ on the battery. These are clearly marked on the battery itself or on its cover. The positive terminal is usually connected to a red cable, while the negative terminal is connected to a black cable.

Finally, check that your jump leads are long enough to reach between the two vehicles¹ safely.

3. Line up both cars closely

Move the donor car to face the front of the vehicle with the flat battery or alongside it.² The idea is to get both cars close enough so the jump leads can reach between them while ensuring they don’t touch.

4. Ensure both cars’ engines are completely switched off

To be safe, turn the ignition off in both cars¹ and remove the keys. Put the car in neutral (or Park, for an automatic) and put the handbrakes on.

5. Connect the red jump lead first

Now, start connecting the jump leads to the battery in the correct order.¹ The most significant danger when jump starting a car is incorrectly attaching jump lead cables, which could result in a short circuit and the battery could explode.

Flip open the plastic cover (if there is one) and connect the red positive (+) lead to the dead battery’s positive terminal¹ using the alligator clip. Make sure the grip is secure. Second, connect the other end of the red lead to the positive terminal of the good battery in the donor car.¹

6. Connect the black jump lead second

Next, connect the black jump cable to the good battery’s negative (-) terminal.¹ For safety, do not connect the second negative clamp to the negative terminal on the dead battery. Instead, attach the clamp to an earthing point on the dead car away from the battery and moving parts, such as a bolt head on the engine block.

Hold only one jump lead at a time to reduce the risk of a short circuit. A lead can cause a short if it touches another terminal or the car's metal bodywork. When connecting the batteries, keep the leads away from the car's metal parts and from each other until they are securely connected.¹

7. Start the car's engine with the charged battery and let it run for 5 minutes

Start the donor car’s engine keep it running for about 5 minutes. Gently run the car at idle to produce enough speed to charge the dead battery.³

8. While the engine of the charged car is still running, try to start the engine of the car with the flat battery

Now, you can try to start the engine of the car with the dead battery.¹ If it doesn’t start, wait a few minutes before trying again.

9. Let both cars run for 5 minutes

Once the donor car is running, let it run for 5 minutes before trying the flat car. Once the flat car starts, also leave it running for about 5 minutes.¹

10. Turn off both cars

Switch both cars' engines off.

11. Disconnect the jump leads in the following order:

• Remove the black lead attached to the car with the flat battery
• Remove the black lead connected to the vehicle with the charged battery
• Remove the red lead attached to the donor car
• Then remove the red lead from the previously flat car.¹
  
  Do not let metal components touch each other.

12. Restart your car and leave it running for around 30 minutes before driving it

Once you have restarted the engine, the battery will take some time to recover. Drive it around for 30 minutes ¹, but turn off equipment such as the radio to allow the battery to recharge completley.

How to jump start a car with a portable battery pack

1. Check the battery pack is fully charged

You might want to keep a battery booster pack in the boot in case you can’t find another vehicle to help; and you need to jump start the car by yourself. Remember to keep the battery pack charged. If you have left it in the boot for six months, the chances are it will be flat.

2. Place the battery pack on the ground, close to the vehicle

Put the battery booster pack on a flat surface, preferably the ground ¹. It should be close to the vehicle so the jump leads can reach the battery.

3. Locate the vehicle battery

Open the bonnet to find the vehicle battery’s location. It could be under the bonnet or in the boot. Also ¹, check the battery voltage. Most batteries are 12V, but the owner’s manual should tell you. Read the instructions with the battery pack to check whether it’s appropriate for a 12V or whatever voltage battery you have. The owner’s manual will tell you if you’re unsure.

4. Connect the positive red jump leads

When you’re ready, put on gloves and goggles for protection. Turn off the ignition. Connect the positive (+) jump lead with the booster pack to the flat battery's positive (+) terminal [41].

5. Connect the negative black jump leads

Next, connect the negative (-) black jump leads to an earthed bare metal  part in the engine bay.¹ For example, you could use an unpainted metal bolt or bracket attached to the engine block. It should not be near the fuel system or the battery.

6. Switch on the battery pack and leave it running for a couple of minutes

Switch on the battery pack once it’s connected to the dead battery¹

7. Attempt to start the vehicle

Try starting the engine and gently increasing the revs to about 2,000rpm to generate enough power to transfer to the flat battery.

8. Once the vehicle starts, keep the engine running for about 5 minutes

Keep the engine running to make sure it works. At least 5 minutes should do it.¹

9. Switch off the engine, switch off the battery pack, and then remove the cables

Turn off the ignition and the battery pack. Remove the jump leads from the booster pack ¹ in the reverse order that you connected them (the black first, then the red).

10. Restart the engine again

Now, you can restart the engine and drive the car for about half an hour to recharge it. 

How long does it take a battery to charge after a jump start?

It takes about 30 minutes of driving in normal conditions after the leads are off to put some charge into the battery after a jump start and before you stop. Otherwise, you may need another jump start. For a full recharge, you’ll need a proper battery charger and a few hours.

For more useful tips, see: How often should you service a car?

What happens if your car’s not starting after a jump start?

If your car won’t start after a jump start, the battery may no longer hold a charge and need replacing. However, the issue could also be caused by another electrical fault.¹ If you're unsure what's causing the problem, it's best to seek professional help to diagnose it safely.

Will car insurance cover flat car batteries?

Standard car insurance will usually not cover flat batteries – but if you have breakdown cover, this may include jump starting your car.

With Ageas Car Insurance you can drive with confidence, knowing help is available if your policy includes the optional breakdown cover and your vehicle breaks down, including battery-related issues.

Should i notify my insurance provider if i've jump started my car?

No, you generally don’t need to notify your insurer that you jump started your car, so long as it was a typical jump start without any damage or accidents.

However, you should tell your insurer if the jump start was needed following a road traffic accident, if it caused damage to either vehicle, or if you needed professional assistance to recover the vehicle or fix a dead battery.

FAQs

What is the correct order to jump start a car?

1. Connect the red positive (+) wire to the positive terminal on the flat battery
2. Attach the other end of the red lead to the positive terminal of the good battery
3. Connect the black jump cable to the negative (-) terminal of the good battery³
4. Attach the second negative clamp onto a piece of bare metal in the car away from the fuel system and the battery³

What gear do you jump start a car in?

You jump start a car in neutral.¹ Do not put either car in gear.

Do you connect red or black first when jump starting a car?

When jump-starting the vehicle, you connect red jumper cables first, starting with the positive terminal of the car with the dead battery.¹

What happens if i connect the leads wrong?

If you connect the leads the wrong way, this could damage your car’s electrics, create a short circuit and potentially cause sparks.¹ Among the things that could be damaged are the vehicle’s battery, the alternator and jump leads.

Do you keep the car on when jump starting it?

You don’t leave the car engine on the whole time. Both engines have to be off to connect the leads. Once they’re on, you can start the donor car’s engine and run it for five minutes. Then start the flat battery car and run it for five minutes. Finally, switch off the revived car, disconnect the negative lead and check it restarts, before removing the remaining leads.

Does revving help you jump start your car?

You don’t need to rev it. The RAC’s method is to start the donor car and let its engine run at idle for several minutes – this will charge both batteries. Next, run the revived car for around 5 minutes, too. Leaving the engine running does the job.¹

How to safely remove the jump leads

To remove the jump leads safely, take them off the battery in reverse order:

1. Disconnect the black lead to the car with the flat battery
2. Disconnect the black lead attached to the vehicle with the good battery
3. Finally, disconnect the red lead connected to both cars.¹

Can you jump start a car in the rain?

Yes, you can jump-start a car in the rain. It’s not dangerous as most batteries are 12 volts – not powerful enough to injure you in the rain.¹

 

Find out more about the Ageas car insurance.

Sources

1. https://www.rac.co.uk/drive/advice/car-maintenance/how-to-jump-start-a-car/

2. https://preventblindness.org/how-to-jump-start-a-car-battery-safely/

3. https://www.racshop.co.uk/advice/most-common-battery-mistakes-that-could-leave-you-stranded/

4. https://www.halfords.com/motoring/how-to-guides/how-to-jump-start-a-car-guide.html

5. https://www.caranddriver.com/features/a26801962/how-to-jump-start-car/