How to change your car battery

The good news is, with eBay, finding a replacement battery you need is simple. You can enter your reg number to browse the right parts that fit your vehicle, and they're backed by eBay Assured Fit. So, if the eligible part doesn't fit, you can return it for free within 30 days.

We’ve put together a detailed guide to help you carry out the job yourself, but let’s start at the beginning, with how a car battery actually works.

What is a car battery?

A car battery provides the power your car needs to power the engine – its various pumps and ignition systems – and the various other systems in your car, everything from the radio to the ventilation system.

Like any other battery, it works by creating a chemical reaction that produces electricity when you turn the key in your car's ignition. In addition to releasing energy, your car battery can also be recharged using your car's alternator. A healthy battery that's gone flat could be caused by a faulty alternator.

How do I test the health of my car battery?

Some cars will tell you when there is a problem with your battery, or the problem could be diagnosed using a fault reader connected to the car's OBD reader.

A rudimentary way to test your car's battery at home is to turn on the headlights – if they're dimmer than usual, that could indicate the battery is low on charge. If revving your car makes the headlights brighter, it could indicate a faulty alternator because the brightness of your lights should remain steady irrespective of what the engine is doing.

You'll need a voltmeter to check the health of your battery correctly. To do it, switch off your car's ignition, remove the covers on your battery's terminals, connect the voltmeter's positive side (red) to the positive battery terminal to the negative side (black) and then check the voltmeter's reading – a reading of between 12.4V and 12.7V means your battery is healthy.

How do I keep my car battery healthy?

To keep your battery healthy, ensure its terminals are clean and the positive and negative cables are securely fastened to their terminals. Use your car regularly, or if you don't – maybe it's a fair-weather sportscar – then use a trickle charger to keep your battery topped up.

How do I check the age of my battery?

Batteries are designed to last for around seven years, so check the age of your battery, which is usually stamped as code on top of the battery. Different manufacturers stamp their batteries in various ways, but their respective websites will explain how to decipher the coder. Often, the last four digits in the code represent the battery's month and year of manufacture, so 0320 would mean the battery was made in March 2020.

How to remove a car battery

First, you need to know where the battery is located. In most cases, it will be under the bonnet and readily identifiable as a square box with positive and negative contacts coming out the top. Some cars will have their battery located elsewhere, like in the boot or – in the case of mid-engined cars – under the engine cover behind you.

Once the battery is located, your next step is to disconnect the negative terminal, usually marked as '–', using a spanner to loosen the bolt. Once you've removed the bolt, you'll be able to twist and lift the cable away from the battery. You can then do the same to disconnect the positive terminal – usually marked '+' – following the same steps as above. 

With the connections removed, you'll need to remove the bracket that holds the battery in place before you can lift it out. Once the battery is removed, it's worth cleaning the battery tray, which is prone to rusting from coming into contact with the battery's corrosive liquids.

How do I recycle my old car battery?

You can't dispose of your car battery as part of your household refuse, but you can drop it off at recycling centres (the location of which is available on the government website), and battery suppliers often offer a drop-off point for safe disposal of used batteries.

How do I find a new car battery?

We’d recommend eBay Assured Fit. Alternatively, most battery providers can tell you which battery fits your car using its VRN (Vehicle Registration Number), which you can find under the right-hand corner of your windscreen, stamped on the chassis (often on the driver-side sill) and in your car's logbook.

How to install a new car battery

Once you’ve identified and purchased the battery you need, fitting it is a simple process. Simply reverse the process for removing the old battery, starting by placing the new battery into position and locking it in place with the holding bracket. Then reconnect the terminals, positive first and finally negative.

Once the battery is all connected, you’ll be able to test the ignition again, and sit back with satisfaction as the engine starts at the first time of asking.

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