A Guide to Car Batteries

As cars become more complex, so do their batteries. There are so many different types available that you might not know where to start when it’s time to replace yours. If you need advice, this guide is here to help.

What is a car battery?

A car battery is a large rechargeable battery that provides electricity to your vehicle. It looks like a plastic box with two connection points, known as terminals, where it links to the car’s electrical system. On the side of the battery, you’ll find a sticker displaying manufacturer information and the number of years it is covered under its guarantee.

What does a car battery do?

Your car needs a battery to function. Here are three things the battery is responsible for.

1. Ignition

The battery provides electricity to the parts that ignite the fuel in your engine to make it work - namely, spark plugs or glow plugs, depending on whether you have a petrol or diesel car.

2. Starting

When you turn your key in the ignition halfway, you can start using your car’s electrical systems, such as the lights and radio, before the engine is on. The battery makes this possible.

3. Lighting

Your car's interior and exterior lights run using power from the battery. The same goes for any electrical items you plug into the 12V power outlet, such as a phone charger.

This guide explains why your new car's battery will cost more to replace.

How do car batteries work?

Car batteries use a chemical reaction to generate electricity. As soon as you half-turn the key in the ignition, this reaction takes place, and the good news is that it can also be reversed. This means energy can be stored in preparation for the next time you start the engine. However, the battery will lose its charge over time and eventually need replacing.

Find out how much it costs to change a car battery.

What car battery do I need?

There are several types of battery available.

Lead-acid

Lead-acid batteries are among the most common types of car batteries. They are relatively cheap to replace, durable, and often last 20,000 starts or more.

Calcium

Calcium batteries have a longer lifespan than conventional lead-acid batteries, lasting for 30,000 starts or more. They also have more starting power - around 18% from standard ones and 33% from premium ones. However, they’re also more expensive.

Lithium-ion

Lithium-ion batteries are usually found in hybrid and electric vehicles because they can store more energy and charge faster. They are much lighter than conventional lead-acid batteries, and although they are more expensive, they last longer, too - between ten and 20 years.

Nickel-metal hydride (NiMH)

Nickel-metal hydride batteries are mainly used in hybrid cars, though they have been successfully implemented in some EVs. They have a longer life cycle than lithium-ion and lead-acid batteries but also have a high self-discharge rate and are expensive. They generate a lot of heat, which makes them less suitable for electric cars.

Absorbent glass mat (AGM)

If your car uses start/stop technology, you’ll need an AGM or EFB battery. AGM batteries are valve-regulated lead-acid (VRLA) batteries. They can charge up to five times faster and last three times as long as a conventional battery. AGMs often need registering with your car’s onboard computer system when they are fitted.

Enhanced flooded battery (EFB)

Like AGM batteries, EFBs are used in cars with stop/start technology and may need registering with the car’s computer. They use a liquid electrolyte solution but are sealed and provide around 85,000 engine cranks.

How long do car batteries last?

• Conventional lead-acid batteries typically last three to five years, providing around 20,000 engine starts.

• Calcium batteries usually provide 30,000 starts or more.

• Lithium ion batteries have a lifespan of ten to 20 years.

• Nickel-metal hydride batteries last around eight to ten years.

• Absorbent glass mat batteries usually last six to ten years.

• Enhanced flooded batteries have a lifespan of around six years.

How do I charge my battery?

The alternator should recharge your battery as you drive along, which means you don’t usually have to think about charging it yourself (in a petrol, diesel, or non-plug-in hybrid car). However, you can try jump-starting it or using a charger if it is flat.

Sometimes, a flat battery indicates that you need to book a replacement. Here are all the reasons why batteries die.

How to install a new battery

Replacing a conventional lead-acid battery isn’t difficult as long as you do your research and follow safety precautions. This guide explains how.

For electric vehicles and those with stop/start technology, a battery replacement is more complex and a job best left to a professional. Electrical systems can easily get damaged if you don’t know what you’re doing.

Fortunately, it’s easy to find a reliable local mechanic to do the job for you using FixMyCar.

Signs your battery is faulty

There are usually several signs when your battery is about to fail.

Battery warning light

The first and most obvious is the battery warning light. When you see it illuminated on your dashboard, it's time to check your battery.

Car struggles to start

If your car struggles to start, especially if it’s not cold, this could be a sign of a problem with the battery. Many garages offer a free battery health check to provide information about the condition of your battery and offer advice about the next steps.

Headlights are very dim

Another sign that there might be an issue is that your headlights suddenly become dim, even when the engine is on. When your battery is low, it can often supply enough power for things like the radio but struggles with bigger drains on its power, such as the headlights.

Car starts but then stops straight away

This is one of the most frustrating things that can happen, especially on a cold and frosty morning. The battery has enough power to start the car but not enough to be left idling.

Here are eight reasons your car won't start.

Tips for prolonging battery life

Here are our top tips for extending the life of your battery.

• Choose the correct battery for your car and have it fitted by a professional.

• Drive your vehicle regularly, and try to fit in a longer journey (30 minutes or more) each week.

• Inspect the battery often and make sure it’s clean.

• Protect it from the cold by parking in a garage if you can.

• Switch off non-essential electrical accessories.

• Book a battery check.

• Make sure the lights are switched off when you exit your car.

• Avoid leaving your car for too long without being used.

Why does my battery keep dying?

Batteries can die for many reasons. Cold weather and lack of use are often to blame, but if your battery repeatedly goes flat without any apparent explanation, it’s a sign that you need to replace it.

If you found this guide helpful, you might also like:

• How to change a car battery

• How to charge a car battery

• Why do car batteries die?

• Why your new car battery will cost more to replace

• What to do when your car battery is dead

• Top tips for maintaining your car battery

• How much does it cost for a mobile battery repair?

• How much does it cost to change a car battery?

• How does a car work?