A guide to car batteries

How does a car battery work? And how long will it last? Here’s our guide to the ins and outs of car batteries and what to do if yours dies.

How does a car battery work? And how long will it last? Here’s our guide to the ins and outs of car batteries and what to do if yours dies.

Daniel Hutson
Motor insurance expert
6
minute read
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Posted 14 JANUARY 2020 Last Updated 27 APRIL 2022

What does a car battery do?

A car battery supplies electricity to your car’s starter motor, which is what gets the engine going. The battery also powers up the radio, lights and on-board computer.

Dead car batteries are one of the major causes of car breakdowns. And one of most common reasons for battery problems is people leaving the lights on while the engine’s not running. This is easily done, especially if you’re a new driver.

How much does a car battery cost?

How much you pay for your battery depends on what kind you need and where you buy it. Car batteries vary enormously in price – you could pay anything between £45 and £290. But don’t forget, you’ll also need to factor in the cost of fitting it.

Can I change a car battery myself? 

It’s never a good idea to change your own car battery. Knowing which type of battery to fit takes expertise. If you make a mistake, it could not only damage your car’s electrical system but could well be dangerous, as well as expensive to put right. Only a trained mechanic will be able to tell if the fault is with the battery or the car itself.

How long do car batteries last? 

Assuming you buy the right battery for your vehicle make and model, your car battery should last around five to seven years. 

But long drives help car batteries stay in optimum condition – if you make lots of short trips, you may find your battery wears out faster. How you treat your car, and the outside temperature, will also affect your battery’s lifespan.

How do I know if I need to replace my car battery?

Here are a few tell-tale signs that your car battery needs replacing: 

How do I avoid running down my car battery? 

If you want to maximise your car battery’s lifespan, there are a few ways you can do it:

  • Don’t use the radio or other electronics when the car’s engine is off
  • Take a look at the battery. Is there gunk on the cables? If so, there are products you can buy to remove it
  • Avoid making lots of short journeys
  • Use a trickle charger to stop your battery going flat if you don’t use your car regularly
  • When you leave the car, check the internal lights and headlights are turned off. Also switch off any electronics, such as dash cams, which might drain the battery.

What do I do if my car battery dies? 

Provided it’s not completely dead, you can try to charge your battery using a car battery charger that plugs into the mains.  

If the battery is completely flat, you can try jump-starting the car. For this, you’ll need some jump leads and a driver willing to attach them to their own car. Once you’ve started the engine, keep driving for at least half an hour until your battery has charged. 

If neither of these methods works, it’s time to get a mechanic to diagnose what the issue is and fix it - replacing the battery if necessary. If you have breakdown cover, you may be able to call your provider for help.

Why has my car battery died? 

There are a number of reasons your battery might not be working: 

  • You haven’t driven your car in a while
    Cars need to be driven regularly. If you go away for an extended period, you may come home to find your car’s battery is flat.
  • You’ve left the radio or lights on without the engine running
    Forgotten to turn your car’s lights or heater off, or shut down the infotainment system? Again, you may return to find your battery’s dead.
  • Your battery is in poor condition
    How old is the battery? If it’s been with you more than five years, it may be time to get a new one. 

Remember, the problem might not be with the battery. If you can’t start your car, the first thing you should do is check the headlights. If they work, the problem may be with your car’s electrical components rather than the battery. Either way, you’ll need to call the garage.

Frequently asked questions

How long does it take to charge a car battery?

How long it takes to charge your battery will vary, depending on your car’s make and model and how powerful your charger is. If you’re in a hurry, you could probably do it in two to four hours. But ideally you should opt for a slower, overnight charge.

If you’ve jumpstarted your car, then driving it for half an hour or so should do the trick.

How to start a car with a dead battery

If your car won’t start and the problem is a dead battery, the easiest solution is to jumpstart it.

To jumpstart a car, you’ll need a pair of jump leads and access to another car with a working battery. Once you’ve tracked those down, here’s what to do:

  • Check your battery. If it’s cracked or leaking acid, don’t try to charge it.
  • Switch off lights, windscreen wipers, air con, and anything else that might drain your battery.
  • Park your car next to the other car and make sure the handbrakes are on and the ignition is off.
  • Using the red jump lead, connect the working battery’s positive (+) terminal to the flat battery’s positive (+) terminal.
  • Using the black jump lead, connect the negative (-) terminal of the working battery to an earthing point.
  • Keep both engines off, then after a few minutes, start the working car’s engine and let it run for one minute.
  •  Start the car with the flat battery.
  • Leave both cars idling for 20 minutes or so, then take your car for a drive – ideally for at least half an hour. By that point, your battery should be charged, which means you can switch off the engine without worrying.

Can a car run without a battery?

Although in theory a car could run without a battery, using the alternator to power the engine, you wouldn’t be able to start it without one.

What does it mean if my car’s dashboard battery light is on?

If your car’s dashboard battery light is on, it doesn’t necessarily mean your battery is on the blink. It could be an electrical fault, or a problem with the charging system. Either way, it’s a good idea to call a mechanic and get it checked out.

What should I do with a dead car battery?

Batteries contain lead dioxide and sulphuric acid, making them extremely harmful to the environment. That’s why you should never simply throw them in the bin. If you can’t get your mechanic to take yours for you, take it to your local recycling centre.

How does the weather affect my car battery?

When the weather is extremely cold, your battery can lose power as it has to work harder to keep you and the car warm. You often see this with electric cars, which see their batteries die far more quickly in winter than summer.

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