How to jump start a car

There’s nothing more frustrating than getting in the car and turning the key, only to hear the engine splutter and give up (especially when you’re already running late!).

There are multiple reasons why this happens but one of the most common is having a flat car battery.

You might expect older, more worn cars to need jump starting from time to time but newer cars also often need a helping hand, as the built-in technology modern cars have can drain the battery very quickly.

Luckily, if you have a set of jump leads (also called booster cables) to hand, it’s not hard to jolt your car back to life.

What is jump starting and how does it work?

Car batteries are fairly difficult to drain because opposite to most things, driving the car is what charges the battery.

The added benefit is that if you do end up with a flat battery, all you need to do is provide enough power to get the engine going again and the car will take care of the rest.

When you jump start a car, you’re basically using the other car’s battery to recharge yours just enough for it to power up the engine. Once the engine’s on, the car will begin to charge itself again.

Before you start

First of all, knowing how to jump start a car is no use without any jump leads so if you don’t own a pair already, you can usually find them in your local supermarket, Halfords, or can even order them from Amazon and other online retailers.

Aside from jump leads, the only other thing you need to jump start a car is another car with a fully charged battery of a similar voltage to yours.

That might sound like a tall order but if you’re at home, hopefully a neighbour will be willing and if you’ve broken down on your way somewhere, more often than not a good samaritan will stop to help.

And remember never to try and jump start a hybrid or electric car and never use one to jump start your own car, as they can be damaged by the process.

Jump leads rolled up

Safety precautions

• Batteries produce flammable gases so remember never to smoke near either car.
• Never try and jump start a car if either battery is damaged or leaking, call a mechanic instead.
• Don’t use damaged jump leads.
• If you’re wearing anything metal (like jewellery) make sure to remove it before starting and don’t let it touch the battery.
• Take off any loose items of clothing (e.g. a tie) before reaching under the bonnet, in case they get caught in the engine.
• Disconnect the jump leads if at any point they get too hot.

Step-by-step guide: How to jump start a car

1. Park the cars next to each other, close enough that the jump leads can reach both but far enough apart that they’re not touching each other.

2. Turn the engines off and remove the keys from both cars.

3. Locate where the positive terminal is on the battery of the car that works – like any battery, it should be marked with a + symbol.

4. Using the red jump lead, clip one end to the terminal.

5. Clip the other end of the red jump lead to the positive terminal on the car with the flat battery.

6. Make sure the jump lead is positioned so that it can’t fall into the engine and check that the clips are secure.

7. Connect one end of the black jump lead to the negative terminal (marked with a – symbol) on the working battery.

Positive battery terminal

8. Find the earthing point on the car that won’t start. If your car doesn’t have a dedicated earthing point, use any bit of solid, unpainted, metal on the engine block or chassis.

9. Keeping away from the battery and fuel system, attach the spare end of the black cable to the earthing point – don’t worry if there is a small spark as you do so.

10. Wait a couple of minutes, then go to the car that works and turn the engine on, letting it run for around two minutes.

11. Try to start the engine of the car with the flat battery. If it won’t start, leave it a few more minutes and try again.

12. Once the engine has started, let it run for around five to ten minutes while the battery charges.

13. Turn off both cars and disconnect the jump leads in the opposite order to how you put them on – starting with the black lead on the earthing point and working backwards. Take extra care to not let the leads touch each other, either car, or you (unless you’re touching the insulated part).

14. Restart your car and off you go! Try and drive for at least thirty minutes to let the battery continue charging and avoid having to repeat the whole process.