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

If your car is slow to start, won’t start at all or the head lights are dim, the chances are you have a flat car battery.

While it’s possible to call a mechanic or your breakdown recovery provider to come and change your car battery for a new one, you could save yourself both time and money by sourcing and replacing the car battery yourself.

This might sound like a daunting task, but changing your car's battery is fairly straightforward. It only requires some basic tools and knowledge.

In this guide, we’ll help you determine if you have a flat car battery, as well as walking you through the process of removing and fitting a replacement. The guide also covers choosing the correct replacement battery, top tips to help you care for your car battery and how to dispose of an old battery safely.

What is a car battery?

A car battery is a rechargeable source of energy that provides electrical power to help jolt the car into life when you turn the ignition key. It also powers various electrical systems like the headlights, air-conditioning or touchscreen infotainment systems.

Electric cars and hybrid cars have larger batteries that are engaged in actually powering the wheels of the car but we’re concerned here with the 12-volt batteries found in traditional petrol and diesel cars that run the electrical systems. 

What are the symptoms of a flat car battery?

If your car’s 12V battery is dead, this will quickly become obvious as your car will fail to start, and the on-board electronics may also refuse to work. 

There are some tell-tale signs that your car’s battery has gone flat, these include:

• Nothing happens when you attempt to start the engine (sometimes you may hear a clicking sound from the starter motor).
• The engine manages to start but then suddenly dies without warning.
• Dashboard lights appear very dim and/or a number of warnings begin to show.
• On-board electrical systems refuse to work.

Obviously, a car that won’t start is a huge inconvenience, so looking out for the symptoms that can occur before the battery fails can help to prevent an incoming breakdown.

If your battery is starting to go flat, you may experience the following:

• A red battery-shaped dashboard warning light appears.
• The engine struggles to start (especially in colder weather).
• Lights are dimmer than they should be.
• On-board electronics, such as windows, are slow or have failed.
• The battery is becoming hot when the car is in use (never touch a hot battery).

How long do car batteries last?

Most 12V car batteries have a lifespan of between three and five years, but this varies depending on a number of factors such as the external climate, original battery condition and vehicle maintenance.

While car batteries of today have a longer lifespan than those of the past, a modern battery doesn’t only have to crank the engine but there are a host of complicated on-board computers and ECUs to power, too. Add to this features like high-power speakers, electric windows and heated seats and the drain on your battery is huge, and that’s before you put your phone on charge.

Stop-start systems might be good for fuel economy and the environment, but they help to give your battery a proper pasting too.

We’re only talking about a car’s 12V battery here. Hybrid cars and electric cars also have much larger and more powerful batteries that either assist an engine or power the car alone, but most do still have a 12V battery, though. Hybrid and electric car batteries are discussed further down this page. 

How to check a your car battery’s health

As part of your routine maintenance checks, it’s good practice to keep an eye on your battery’s overall condition. There are a number of ways to carry out this inspection, and every process is easy to do. Here are some of the best ways to check your car battery’s condition, all of which should be carried out with the car switched off.

Built-in indicator

The vast majority of modern 12V batteries now have a built-in condition indicator to make checking it a very quick and easy task to do. Sometimes referred to as a ‘magic eye’, these indicators are a small circular symbol that sits within the top of the battery. If the indicator is green, the battery is in good health, if it’s black, you should only need to recharge. However, if it’s red, the battery is dead and it’s time to source a replacement.

Visual inspection 

Take a close look at your battery and check for dirt or corrosion on the two terminals. This problem can disrupt the circuit, but it can potentially be fixed by simply disconnecting the battery and brushing away any grime. Also look out for any bulging in the battery’s casing, if you spot this, it could also be leaking acid so be very careful and do not touch it. This problem can be dangerous so the battery must be removed and correctly disposed of as soon as possible. If you’re unsure about safety, consult a professional.

Age

Time takes its toll on all car components and batteries are no exception. Your battery’s lifespan will be displayed on the label along with the manufacturing date. If your battery is past its prime, it’s time to replace it.

Voltmeter

Basic voltmeters can be picked up cheaply from most hardware stores and they’re fairly straightforward to use. First connect the positive wire to your battery’s positive terminal (this is usually red in colour) and then the negative wire to the earth terminal (this is usually black in colour). Once connected, the voltmeter should read around 12-12.7 volts. If the reading is any lower than this, your battery either needs a top-up or it’s struggling to hold a charge. 

Changing a car battery: a step by step guide

1. Locate the car battery

Most car batteries are found under the bonnet, however, in some models they are located under the footwell or in the boot instead. If you are unsure then check your owner’s manual. 

2. Disconnect the negative terminal FIRST, then the positive terminal

When you’ve found the battery, make a careful note of which terminal is which. Once you are ready to remove the old battery, disconnect the negative terminal ( – ) first by undoing the nut or bolt which secures the terminal and then by gently pulling the connector away. 

Once this is disconnected, you can then disconnect the positive (+) terminal. Be sure to do it in this specific order, otherwise you could cause an electrical short or sparks that can cause damage and injury. 

3. Remove the old car battery from the battery tray

Once both terminals are safely removed, keep the connectors away from each other, as well as anything made of metal and remove any clips holding the battery in place, then lift or slide it out of its tray. 

There may be additional obscured brackets or bolts holding it in place so do not force it. 

4. Clean the battery tray and terminals

Once the battery is out, it’s always worth giving the tray a good clean and removing any corrosion or residue. Rinse with clean water and dry thoroughly afterwards.

Give the terminal connectors a clean with a wire brush or some terminal cleaner. If you do this, remember to apply some terminal grease after to help prevent corrosion and ensure a good connection.

How to fit a car battery

If you’re fitting a new car battery or reconnecting the old one, simply reverse the steps above.

Simply place the car battery into the cage, fasten any connectors or clips which hold the battery in place and reconnect the terminals. Make sure you connect the positive terminal first, then the negative. 

Test the new car battery

Once the new battery is hooked up, It is likely that you will now need to reset any electronics inside the car – such as the clock or infotainment system. Some infotainment systems may ask for a security code, and this should be located in or alongside your owner’s handbook. 

You may need to keep the car running or take it for a drive to reset the car's ECU, so don’t be alarmed if the warning lights on the dashboard remain illuminated and don’t disappear immediately. 

How to dispose of a car battery

Now you’ve removed your old car battery, you will need to dispose of it.

Car batteries can be very hazardous to the environment if they are not disposed of properly. In fact, it’s illegal to simply chuck a car battery in the bin, not to mention potentially dangerous. Fortunately, the process for correctly and responsibly recycling car batteries is easy. 

Several battery recycling centres, car parts stores and garages offer a battery-disposal service, many of which are free of charge. Once you’ve handed over your old battery, these service providers will safely drain the battery, remove any other harmful materials and then recycle as much of it as they can. 

How to choose the right battery for your car

Finding the right battery for your car isn’t just a case of ‘one size fits all’, but finding the correct fit needn’t be intimidating. Car batteries come in various sizes and types, and each battery has a three- or four-digit code such as 075 or 096T. This code indicates the size, power rating and terminal positions of the battery, among other things, and will help you find the correct replacement.  

Though the traditional lead-acid battery is still fairly commonplace, different cars require different battery types depending on their on-board systems etc. If your car has stop/start, the battery will need to be tuned with the on-board computer, so fitting these particular variants may be a job that’s better suited to a professional. Also, If you fit the wrong type or size of battery to any vehicle, it could cause a severe lapse in performance. As a general rule, always fit the same type and size as the manufacturer’s original. 

Although this may all look confusing, a quick look at the owner’s manual should have all the information you need. Additionally, while the internet is a valuable resource, many suppliers’ websites will allow you to enter your registration number to find the correct specification for your vehicle. 

Plus, if you shop around online, you’ll have a good chance of finding a big discount, along with the added bonus of having your heavy new battery delivered to your door.

Top tips for caring for your car battery

Now that you’ve splashed out and installed a new car battery, there are several ways you can protect your investment and potentially prolong its lifespan, especially if you don’t use your car that often.

Use a car battery charger

Many modern battery chargers have sophisticated programmes to maintain the level of charge – which is why many classic car owners swear by these products. Car battery chargers are the quickest way to top-up your car's battery. Simply connect the connectors to the right terminal and plug into a three-pin socket. This can be done while the battery is still installed in the car.

Use a smart battery trickle charger 

These smart trickle chargers vary the current that they pump into the battery in order 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. There are different variants of trickle chargers, including ones which clip directly on to the cars battery, or even solar chargers which plug into the 12V socket in the cabin.

Can you change the battery in an electric or hybrid car?

Electric cars and hybrid cars have the same 12V battery as hybrid and combustion models for powering the same types of on-board electronics, such as windows and infotainment systems. You can indeed change this battery using the same process as mentioned above.

However, you must never go near the main battery pack or any other components that are powering the EV or hybrid itself. These carry an extremely high amount of electricity and can be very dangerous or even fatal if they are interfered with. Always consult a trained professional for any work on these components.

Jump starting

If you’re away from home (or a garage) and find yourself with a flat battery, a jump start could help you to get moving again temporarily. You’ll either need a kind person with another car or your very own jump start pack. 

Thankfully, jump starting a car is fairly straightforward, and we’ve covered everything you need to know on jump starting a car in this full in-depth guide.

Need to top-up your battery? Find out more about the best battery chargers…