How to jump start a car
If you’re unfortunate enough that your car fails to start, it might need to be jump-started. But, what is jump starting?
The Cazoo editorial team
Published on 24 October 2025 | 1 min read
If your car fails to start, it could be due to the battery going flat, which then might lead to your car having to be jump-started.
Jump starting is an easy and effective way to start your car if it has a flat battery. It works by using power sourced from another vehicle with a good battery and a set of jump leads, which pumps power from the car’s good battery into your car’s flat battery.
However, there are some precautions that you need to take before you jump-start a vehicle, as it can be dangerous if you don’t know what you’re doing. Some experts recommend that if your car’s battery goes flat, and you haven’t got anywhere to charge it, you should call out professional mechanics to sort the problem out.
If you intend to jump-start the car yourself, here is our handy guide to everything you need to know about jump-starting a car.
How to jump start a car
Firstly, if you plan to start your car’s flat 12-volt battery with someone else’s car, you need to make sure that their vehicle also has a 12-volt battery and it’s fully charged.
Then, you’ll need to line-up both cars together, within distance that their batteries are in easy reach of each other. Also, don’t forget to keep the handbrakes on and the cars’ ignitions are switched off.
Jump leads consist of two cables, the red, as the positive terminal, and a black, which is the negative. Use the red cable to connect the car’s good battery’s positive terminal to the flat battery’s positive terminal. Make sure that the ends of the red and black cables never touch each other too, as this could create a spark or a fire.
Then, take the black cable and place it onto the negative terminal of the good battery, and attach the other end to the earthing point (which is the unpainted metal on the engine block or chassis) and keep the cable away from the flat battery and fuel system.
After a few minutes, turn the car with the working battery on, and let it idle for a minute. Next, turn on the car with the flat battery and leave both cars to run for around 10 minutes, which will allow the battery to recharge and gain its power back.
Finally, turn both cars’ engines off, and reverse the process. Make sure that both leads don’t touch each other or the cars, as this can also lead to a spark or fire.
After that, try and start your car on its own, as there should be enough power in the battery to allow it to start up on its own power. If it still refuses to start, it could be something more serious that will need to be looked at by a professional.
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What equipment do I need?
When jump-starting a car, there are a few tools that you need to make the process run smoothly.
You’ll need to make sure you’re as safe as possible, so bring a pair of rubber gloves to protect your hands and goggles to protect your eyes, just in case any sparks do fly up.
It’s also worth noting that high-vis clothing might be a good idea to have on hand, just in case you need to jump-start your vehicle at the side of the road.
Most importantly, get a pair of good, working jump leads and ensure that the vehicle is within reaching distance of another car with a healthy battery.
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Can I use a battery booster?
A battery booster is a great alternative to jump leads when it comes to jump-starting your car.
A battery booster is a portable and self-contained battery pack that provides electrical charge to a vehicle’s battery.
To use a battery booster, make sure that it’s in a stable position, as you don’t want it to fall into the engine bay. Then, just like with jump leads, it will have a red positive and black negative cable.
Connect the red cable to the positive terminal of the battery and the black negative cable to the earthing point - the same as jump leads.
Once the battery pack is connected to the battery, switch the unit on and power will be immediately sent into the battery. After that, try and crank your car’s engine and it should fire into life. If it doesn’t after a few attempts, then there could be a more serious problem that will need to be looked at by a professional.
Once the car is on and running, you’ll need to disconnect the battery booster, which you do by removing the leads in reverse order to how you connected them. Always remember to disconnect the black negative cable before the red positive cable, first.
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What causes a car’s battery to go flat?
There are several reasons why a car’s standard 12-volt battery can go flat. Simple things such as leaving the interior lights on, side lights, head lights and hazard lights flashing can drain a lot of power from the vehicle’s battery.
Leaving the ignition on for long periods of time can also sap power from the battery, while leaving windows down can also have an effect.
A car’s 12-volt battery is made up of cells with lead plates, and if those cells begin to fail, it will make it harder for the vehicle to turn over. If you notice that your car is taking one too many cranks to start up, then it’s best to get the battery tested through a voltmeter reader.
A voltmeter reader will test to see how many volts the battery is making, with a healthy unit reading 12.6 volts. If your car’s battery is reading less than 10 volts, then it needs to be replaced.
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What do I do after I’ve jump-started a car?
After a car has been jump-started, we’d recommend that you take the car out for a drive that lasts around 30 minutes.
Driving along the motorway will really benefit in putting power back into the battery, while driving on country A and B roads will also be beneficial.
What you shouldn’t do is take your car out for a very short journey through towns and stop-start driving. This won’t put enough power back into the battery, which could run the risk of it failing to start the next time the car is cranked over.
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