Latest car guides

August 18th 2021 info

Car batteries are an essential part of all cars. Most drivers know what a car battery is, and most know how to change one too. However, not everyone is aware of how car batteries work, how long they last and the warning signs that one is breaking.

How does it power the engine and in-car electronics? How important is it? Should you know more about it? Below, we explain what a car battery is, how they work and what to do if you run into problems.

How do car batteries work?

Car batteries have one essential role: supplying a power source to start a car. Sure, it may power our car radios and other electronics too, but nothing quite as important as getting the car running.

So, how does a car battery work? Well, much like other batteries, it converts chemical energy into electrical energy. The name of this reaction is known as the lead-chemical reaction.

Each car battery consists of lead and dioxide plates that float in sulphuric acid. These plates are in a battery’s 12 cells. After switching on a car engine, a reaction occurs between the lead and dioxide, catalysed by sulphuric acid. Turning on the ignition “tells” the battery to start this reaction.

The reaction produces electrons. These electrons form electricity, which moves to the starting motor. The battery also powers the spark plugs.

This process provides the engine with ample energy to start the combustion process. However, the car battery isn’t responsible for maintaining this process. Instead, a car alternator maintains the process. The role of the alternator is why jump-starting a dead battery works; the battery only begins the process.

How long do car batteries last?

“How long do car batteries last?” is a difficult question to answer. Their lifespan varies depending on environmental factors such as climate, mileage, driving style and electronics use.

Broadly, batteries last between 3 and 5 years. However, if you frequently take short trips, drive fast or have a host of electronics on during your commutes, then that could be significantly shorter.

To better maintain your battery, try to avoid having lots of electronic devices on at one time. Don’t think about changing your commuting or driving habits for the sake of a battery, but maybe put the phone charger away when the sat-nav is on.

If you’re asking, “how long does a car battery last without driving?” then the answer is significantly shorter than 3-5 years. When driving, the alternator charges the battery. Without this charge, a car battery lacks the energy to start the ignition process.

In a non-driven car, a perfect car battery can only last 2-3 months.

How to check a car battery

Many drivers have been caught out by a flat battery, even more so while our cars sat on the driveway during lockdown. However, you can regularly check your car battery to ensure this doesn’t happen to you.

Before we explain how to check a car battery, you need to know when a car battery needs to be replaced.

Warnings signs that your battery is on the way out is a decrease in performance. Of course, if you hear the “clicking” sound coming from a battery, then that means it’s already dead.

Unfortunately, without equipment, there isn’t much you can do to test a car battery’s health. The best a driver can do is ensure it is connected properly.

To check a car battery, you need a car battery tester. These are readily available and you can find one for roughly £20. These test a car battery’s health by checking its voltage.

Instructions will differ slightly on a product-by-product basis, but for most car battery testers, you will need to:

  1. Turn off the engine.
  2. Attach the red lead to the positive terminal.
  3. Attach the black lead to the negative terminal.
  4. Wait for the voltage to be recorded.

Now, the voltage gives an excellent indication of a car battery’s health. You will want to see a voltage higher than 12.4v. Ideally, it should be 12.7v.

If it’s under 12.4v, give your car a short drive and check it again with the engine off. Test it again after it has been charged by the alternator.

If the reading is still low, then you will need to charge or replace your car battery.

How to charge or replace a car battery

You can buy a car battery charger from most automotive stockists and stores. We’d recommend researching which charger is best for your car model, either through the manufacturer’s website, instructions or via an independent garage.

Before charging, always read the instruction manual of both your car battery and the car battery charger. We’d also recommend buying an automatic car battery charger, as this switches off once the optimum voltage has been achieved.

To charge a car battery, simply:

  1. Ensure the engine is off.
  2. Affix the charger ports to positive and negative terminals. Only attach them to the terminals.
  3. Ensure the charger cables are untangled. Coiled-up cables could cause overheating issues.
  4. Turn the car battery charger on. Do not turn the charger on before the cables are properly affixed.
  5. If you have an automatic charger, it will switch off when the car battery reaches optimum charge.
  6. Test the battery again to ensure it has been fully charged.

Changing a car battery isn’t worth the risk of doing it at home. To change a car battery, consult a professional at your local garage. It may look easy, but if you make a mistake, it could mean trouble for your car and your wallet.

Reliable used cars

When you buy with, you don’t have to worry about dodgy batteries. We only trade with trustworthy dealers in the UK, meaning you don’t need the knowledge on how to tell if a car battery is bad before buying.

Browse our full range of used cars from across the UK today.

Latest car guides

up to 140,000 quality used cars from over 2,200 trusted dealers

We'll use your criteria to show you personalised quotations to suit your needs.

are you sure?

you’re about to remove this vehicle from your list. Are you sure this is what you wanted to do?

no, keep it

We'd like to keep you up-to-date!

We'd like to send you some occasional news, reviews and offers. We also have some trusted partners who'd like to do the same. Please choose from below, what you are comfortable with.

Email & SMS

Don't forget to create an account or sign in to save vehicles to your profile.