Flat battery? You're in good company - it's the most common cause of roadside breakdowns.

Using a set of jump leads could get you back on the road quickly. However, you need to ensure you understand how to use jump leads safely, since any mistake could be dangerous, or may damage your vehicle's electronic components.

Read your car's handbook first before attempting to use jump leads

Disclaimer: This article provides a basic overview of how to jump start a car using jump leads or a jump start pack

Neither startrescue.co.uk nor Call Assist Ltd. will be held responsible for any damage that occurs to your vehicle as a result of reading this article.

It is your responsibility to read the applicable section in your vehicle's handbook or, if you do not feel comfortable carrying out the jump start yourself, to enlist the help of a professional mechanic.

Before jump starting a car with leads...

Batteries release flammable gases, so it’s crucial to remember:

  • If the battery appears to be damaged or leaking, do not jump-start the car.
  • If your jump leads are damaged, do not use them - find another set.
  • Ensure nobody smokes nearby while using the jump leads.
  • Ensure there are no naked flames nearby.
  • Ensure no metal objects touch the battery. Remove Jewellery, rings, watches etc. - indeed anything made of or containing metal.  If you touch either battery with a metal object it could cause a spark - or the battery may even explode.
  • Remove any loose clothing so it does not get caught in any moving parts.

Here’s a step-by-step guide on how to jump start a car with leads:

How to use jump leads:

In order to jump-start your car you need a working car with a similar engine size to yours. Ensure the voltage of both is the same; most cars feature 12V batteries.

You will also need a set of jump leads in good working condition

Ensure you use jump leads with suitable surge protection.

You should also wear a pair of safety goggles when using jump leads to start your car, in case of any sparks/explosions.

Park both cars near each other  

Open and secure the bonnets of each car, then ensure all electronics are switched off. The best way to guarantee this is by removing the keys from the respective ignitions. Ensure both handbrakes are on.

Now let’s look at how to connect jump leads…

Connecting jump leads - How to connect jump leads:

The correct order to attach jump leads to your car is as follows:

  1. Attach one end of the red lead (positive +) to the positive terminal of the working car.
  2. Now attach the other end of the red lead (positive +) to the positive terminal of the car with the flat battery.
  3. Now attach one end of the black lead (negative -) to the negative terminal of the working car.
    Note: Some modern vehicles advise you to connect the negative terminal to an earth point. Before attaching the black negative cable to any vehicle, always refer to your vehicle handbook to confirm where to attach the negative jump lead; whether you should be connecting the black cable to either an earth point or a battery negative terminal.
  4. Finally, you need to attach - or earth - the other end of the black lead (negative -) to a solid metal fixing that is not painted, on the car with the flat battery. This might be a bolt or bracket on the engine. Some cars have a special earthing rod for this very purpose - check your manual/handbook. This earthing point must be away from the battery, fuel systems and any parts which will move when the engine is turned over.

Ensure all jump leads are firmly attached and wait a few minutes for the voltages to equalise.

Jump starting a car with leads

Next, start the engine of the working car and let it idle for a few minutes, return to the car with flat battery and start its engine too.

If it does not start, wait a little longer with the healthy car's engine running, before trying again.

Using jump leads: How long to leave jump leads on

If the engine does start, leave the engines of both cars running for ten minutes.

Important: If the jump leads become hot, turn the engines off for a few minutes to let them cool off.

Once you have waited ten minutes, turn off both engines.

Disconnecting jump leads: How to disconnect jump leads?

Next, you need to disconnect the jump leads in reverse order. Do this very carefully and ensure the clip teeth do not touch any part of the body work, or each other - because a loud bang is likely to result if this happens (a spark or even battery explosion).

Carefully disconnect the jump leads in the following order:

  1. Black lead from earthing point
  2. Black lead from the negative terminal
  3. Red lead from healthy car on positive terminal
  4. Red lead from newly-charged car's positive terminal

What to do next?

If your battery has run flat there could be a fault with the battery itself, the alternator, or some other component. #

Take your car to a reputable garage and they will be able to assist.

Replacing old batteries

To be on the safe side, it's a good idea to replace your battery once every three years.

Batteries aged four or five years - or older - tend to be unreliable.

Here’s our guide on how to replace your car battery.

How to jump-start a car without jump leads

An alternative to jump-starting your car with jump leads is to use a jump-start power pack.

Jump start power packs are effectively mini portable batteries with their own jump leads attached.

Having ensured that your jump-start box is fully charged:

  1. Check whether your jump-start box comes with integrated cables. Most jump start packs come with integrated cables. However, if yours doesn’t, connect the cables to the correct points — positive and negative.
  2. Connect the positive and negative leads to your vehicle in the same way that you would jump leads (see above for full details as to how to connect the leads to your car).
  3. Once everything is properly connected, switch on the jump-start power pack. After a few minutes, start your vehicle. If your car doesn't start straight away, continue to use the power pack a little longer, to give the battery time to charge.
  4. Once the car has started, turn off the jump-start power pack and remove the leads in reverse order.

Breakdown cover for flat batteries

If you find your vehicle has a flat battery, you have no jump leads to hand, or you’re not confident in using jump leads, breakdown cover from Start Rescue will get you started.

With our 3 Star packages we also provide Home Assist, covering instances of a flat car battery at home.


Get a quote for breakdown cover