How to change a car battery and choose the right battery for your car


If you Google ‘How to change a car battery’, the results will bring up an extensive range of convoluted and sometimes utterly useless articles on how to replace a dud set of cells. It goes without saying that care should be taken whenever you decide to work on electrical components, especially the high current circuits which are found in car electronics. That being said, all the information required for you to install a new car battery safely is fairly basic and easy to follow.

How long do car batteries last?

Sadly, the life of a car battery is a finite thing, even though modern variants last much longer than they did back in the black and white times. As the amount of technology we all use in the average car increases, so too does the demand on batteries, hence the need for capacity to increase.

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Your modern day battery not only has to crank the engine and create a spark (unless of course you drive a diesel (which runs without spark plugs) but there are a host of complicated, and incredibly useful on-board computers and ECUs to power. Add to this features like high-power speakers, electric windows and heated seats and the drain on your battery is huge.  What’s more, that’s before you’ve plugged your phone charger, laptop and possibly an in-car cool box into the 12v socket!

Modern automated stop-start systems might be good for economy and the environment, but they help to give your battery a proper pasting too. You won’t be surprised to hear then, that flat or dead batteries are one of the most popular callouts for breakdown services.

You don’t have to wait for the inevitable emergency though, because if you keep an eye on your battery’s condition it’s possible to spot the early signs of a potential failure. Look out for clues like dim interior lights, or a sluggish engine turnover, and get your car battery tested at a garage or by an auto electrician. Doing it that way gives you a chance to find the best replacement car battery deal at your leisure, instead of being forced into an expensive distress purchase. A professional battery check should also reassure you that it is indeed the battery at fault, and not another of the car’s electrical systems.

Choosing the right battery for your car

First off, you need to find the right battery for your car; a quick look at the owner’s manual will help here, while the internet is a valuable resource. Many suppliers’ websites will allow you to enter your registration number and then tell you which battery is correct. Plus, if you shop around online, you’ll have a good chance of finding a great deal and you won’t need to lug a heavy battery home from the accessory shop or garage.

Standard lead-acid batteries are still by far the most common, with diesel cars generally requiring more powerful versions, while models with stop/start technology tend to use enhanced cyclic mat (ECM) or absorbed glass mat (AGM) batteries. Whatever type your car was supplied with originally, you should replace like with like; check the manual if you’re not sure.

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Before you disconnect your failing old battery, remember that it powers various features in the car, which are likely to be reset. Do you have a code for the stereo, for example? You may need this to use it again when you connect the new battery.

Disconnecting your old battery

Most batteries are found under the bonnet, although some are under the footwell or in the boot. Wherever it is, make a careful note of which terminal is which and disconnect the negative terminal ( – ) first. Then disconnect the positive (+) terminal, remove any clips holding the battery in place and slide it out of its plastic cage. Be careful; batteries are heavy and cumbersome, and the old one should be disposed of at your local council recycling facility.

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Slide the new battery into the cage and reverse the process, connecting the positive terminal first, then the negative. You’ll now need to reset any electricals inside the car – from clocks to stereo to sat-nav. If your car has stop/start, the battery will need to be tuned with the on-board computer, which is why fitting an ECM or AGM battery is probably a job for a professional.

Care for your car battery

Now that you’ve splashed out on a new battery, you want to protect your investment, and the latest chargers have sophisticated programmes to maintain the level of charge. They’re especially useful if you only use your car sparingly – classic car owners swear by these products.

These smart chargers vary the current they pump into the battery to prolong its life. They can even be left attached to a car for long periods of time, and just top the battery up gently. Plus, if your battery is showing signs of being on its last legs, one of these products might be worth a try first; a smart charger can bring a dying battery back to life.

Emergency jump starting

Another handy investment is a jump start pack. These work like the traditional set of jump leads you run from your car to another vehicle’s battery to get you started if you’ve left your lights on all night by accident, for example. The difference is, you don’t need another car.

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Just charge up the jump start pack, attach the leads to the correct terminals on your battery, and they’ll provide a boost to get your car started. The best systems can jump petrol cars with engines up to 3.0 litres in capacity, and promise multiple starts before they need recharging. They’re handy gadgets to keep in the boot.

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If you do get stuck with a flat battery, here’s our guide to jump-starting your car…


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