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Jumping & bumping: How to start your car if the battery’s flat

Somone calling their car breakdown providerEvery driver who’s ever crouched shivering into their car, turned the key and just got a ‘click!’ but no power in response knows how disheartening a flat battery can be. And this is certainly the season for it – it’s the most common cause of breakdown during a cold snap.

There are a couple of quick fixes, however: the bump and the jump. So we’ve put together a guide showing you how to do both.

IMPORTANT : Before we continue, remember that these are quick fixes to get you out of an immediate scrape. If you have regular battery problems, it’s advisable to get it seen to by a professional or replaced. More importantly, if you are a total novice and not confident in what you’re doing, then don’t attempt these fixes. This is especially true of starting a car with jump leads, as you are dealing with live electrics, which is potentially dangerous.

But if you’re happy that you have enough of a working knowledge of cars to get your hands mucky, then let’s dive in.

Bump-starting your car

If your battery’s flat, then your engine will either struggle when you turn the key for ignition, or simply ‘click’ with no further response. If your headlights are dim or won’t turn on, then that’s a good indicator that you’ve identified your problem.

You can only bump-start your car if it has a manual transmission, so don’t attempt this in an automatic. It’s usually a two-person job, although it can be done alone  if your car’s facing downhill. Although you obviously shouldn’t attempt this on a busy road.

Turn on the ignition, put the car in second gear and keep the clutch depressed. When you take off the handbrake you’ll need to gain some momentum, so you’ll have to get someone to push. If your car’s on a slope then that’s better still, as you can allow it to roll and do it all yourself. When the car is getting towards 10mph, release the clutch for a moment, and hopefully your engine should start. That’s when you get the ‘bump’.

If it doesn’t start after two or three goes, then you’re going to have to resort to other measures. If it does, then keep the engine running for twenty minutes or so to charge up the battery. If your car repeatedly won’t start, it’s best not to resort to bumping every time, as it’s no good for your catalytic converter. If this is the case, get yourself a new battery.

Jump-starting your car

This is definitely a two-person job. Or, more specifically, a two-car job. If you find yourself with a flat battery, then – assuming you don’t have your own – seek out someone with jump leads and a functional battery. Ask a friend, or you may even find that a stranger will be courteous enough to allow you to charge off their battery.

Before you get stuck in, check the condition of the battery. DO NOT EVER try to charge a battery that is leaking, or looks otherwise battered or damaged.

Disable everything in your car that would potentially drain power from your battery. So turn off your headlights, windscreen wipers, heating or air conditioning, stereo and so on.

Park the rescue car so that its battery is as close as possible to yours. This could either mean side-by-side or almost bumper-to-bumper, but they shouldn’t touch. But they need to be close enough to allow some slack in the jump leads.

Jump leads are red and black with crocodile clips at either end, and the positive cable tends to be red, and the negative cable black (although double check with the owner, or the packaging you buy them in).

Take the positive cable, and connect one end to the positive (+) terminal on the working battery, and the other end to the positive terminal on the flat battery. When you do this, make sure you don’t touch the battery terminals with your hands.

Then connect one end of the negative cable to the negative (-) terminal on the working battery, and the other end to a bare metal part of the engine of the car with the flat battery, but away from the battery itself. This is to earth the car. A lot of people think that it’s ok to connect to the negative terminal of the flat battery, but there is a risk (admittedly small, but nonetheless a risk) that this might trigger sparks which could lead to an explosion. So be safe, and connect to a metal part of the engine’s casing, such as the engine mounts or the chassis.

IMPORTANT : DO NOT cut corners by connecting both the positive and negative cables at the same time. This is incredibly dangerous. Furthermore, make sure that you don’t cross red and black, and that the positive and negative connectors do not meet.

Then get your rescuer to start up their car. They should leave it running for about ten minutes to charge up your battery sufficiently.

With the car with the working battery still running, try and start your car. If it doesn’t start first time, allow it to charge for a little longer and try again. How long you keep this up will probably be down to your degree of patience; but, if it consistently fails to start, there will come a point when you know you’ll have to give up and buy a new battery, or call your breakdown service.

If it does start, allow it to run for a while in order to further charge up the battery. After a few minutes, switch off both engines. When it comes to disconnecting the jump leads, take them off in the reverse order from which they were put on. Don’t allow the ends of the cables to touch one another immediately after doing this, as it can create a spark.

If the car did start with the jump leads connected, but won’t start now, then you may not have left the battery charging for long enough. Try again, and leave it charging for longer. There might be a problem with charging, such as if the terminals are dirty. Make sure that there is exposed metal on the terminals, and a good tight connection with the leads.

If it does eventually start independently, leave it running for a good while – possibly driving it home, to a garage where it can be tended to, or somewhere where it won’t be a nuisance if you find it won’t start next time you try.

Again, if any of this sounds beyond you, please don’t attempt it. Get someone who knows what they’re doing to fix it for you.

With that in mind, if you’re not already signed up to a breakdown service, you can compare breakdown cover with Confused.com. We think of everything!

Please watch our 30-second guide for more information.

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Owe Carter

Owe Carter

Owe Carter has been a consumer interest writer for Confused.com since 2007. His career as a scribe began in local press, which saw him hunting ghosts, taking challenges from readers, living as B.A. Baracus for a week, and seeking out Pembrokeshire’s happiest dog.

Twitter: @ConfusedOwe
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