Car Batteries Explained

The combustion engine might be the source of power used to send your car hurtling down the road, but before the wheels start moving, something needs to bring it to life at the turn of a key. That thing is a car battery, a crucial component that no car can live without, and they might be a bit more complicated than you think. Here’s how car batteries work, when you’ll need to replace them and what to do when they run out of juice.

How Long Do Car Batteries Last?

In a similar fashion to the batteries in your TV remote, the boxy battery under the bonnet of your car also has a relatively short lifespan. The average amount of time that a car battery lasts before needing a replacement is believed to be three to five years. 

Many controllable factors can have an impact on the length of time your battery lasts before it dies for good. Regularly suffering through extreme temperatures can knock days (or more) off your battery’s life, as can hooking up external devices to your car via onboard USB ports or other connections. 

There are also other, more widely-known causes of battery damage that, despite going against what the laws of ‘wear-and-tear’ tell us, include making multiple short journeys and leaving the car parked up and switched off for long periods of time. That’s right, not using your car battery will actually shorten its lifespan.

How to Disconnect a Car Battery

If your battery is dead, or even on its last legs, and you want to remove and replace it, you’ll first need to disconnect it from the car. It’s vital to know exactly how to do this in order to avoid damaging the vehicle or, more importantly, injuring yourself. Below, we’ve outlined the steps you need to take to successfully disconnect and extract your car battery:

  1. Turn the car off – You should never try to remove a car’s battery with the power still on, or you run the risk of receiving an electric shock. Once the power is off, pop the bonnet. The latch is in different positions on different cars, but your owner’s manual will show you where it is on yours.
  2. Find the negative terminal – With the bonnet lifted, locate the battery and on it, you should see two terminals, one with a plus (+) symbol on it (usually red) and another with a minus (-) symbol (usually black). As you can probably guess, the ‘+’ is positive and the ‘-’ is negative.
  3. Loosen the nut – Next, find yourself a spanner that fits the nut on the negative terminal. There’s no one-size-fits-all tool here, so we can’t make a suggestion. You’ll have to test them out for yourself.
  4. Remove the negative connector – Once the nut is loose, remove the connector – the cable – and ensure that it does not come into contact with the battery again until you’re planning to reconnect it (assuming you are, that is).
  5. Repeat the process – Go back to step two, but this time, repeat your actions for the positive terminal and connector.

At this point, the battery is free to be removed and recycled if or when you need it to be. It might be locked in place by more fixings, so bare this in mind. Just be aware that car batteries can be deceptively heavy.

How Long Does It Take to Charge a Car Battery?

Charging a car battery is a fairly slow process. Each model will differ, but generally, charging could be done overnight. The strength of the charger makes a huge difference, too. Higher amp chargers could refill the battery in a few hours, but a much weaker charger – 4 amps, for example – could take as long as 24 hours.

However, if you’re looking to find out how long it takes a flat battery to charge by running the car, then rest assured the process is much quicker. If your battery has got just enough in it to get the engine running, then half an hour at the motorway pace should charge it to capacity.

How Long Does a Battery Last In an Electric Car?

The new kids on the block, electric vehicle (EV) batteries are a completely different kettle of fish. Since these batteries aren’t just used for simple electronic functions, but instead for powering every aspect of the car – including its movement – they are built to last for far longer, and under much more strain, than one found in a regular combustion engine vehicle.

As a result, EV batteries can last 10 to 20 years and propel your car over 100,000 to 200,000 miles before giving out. Over the years, you may find the range of your EV starts to lessen, which could be a deal breaker for drivers who are looking to go electric but are concerned about ‘range anxiety’. This puts the lifespan of an EV at around the same amount of time as a regular-fuel car, although as technology advances, battery degradation could be slowed down further.

How to Test a Car Battery

If your car battery has started to become less reliable and you find yourself turning the key over and over before the motor roars into life, it would be a good idea to run some tests. You could wait and see if the battery causes an MOT failure, but these examinations may bring to light defects or degradation with the battery that can’t be seen by the naked eye in advance.

Luckily, there is a device specifically designed for testing the voltage of a battery, which can be purchased from most retailers that stock car accessories. For more accurate testing, it’s recommended to buy one of the more advanced versions that can tell you the specific voltage of the battery.

When the device is attached to the positive and negative terminals of the battery as instructed by the manual, you should be hoping to see a reading of at least 12.4 volts. Anything less than this level indicates that the battery is in need of some extra charge. If this is a regular occurrence, it might be time for a new battery (or at least to get a mechanic to take a look at it). A multimeter, or voltmeter, can also be used in a similar way.

How to Know If Your Car Battery Needs to Be Replaced

Even if you don’t have access to testing devices, there are some noticeable changes to the performance of any car that can indicate a failing battery. As we’ve mentioned several times, the most obvious of all is the failure for the engine to start when the key is turned in the ignition.

However, more subtle signs of a dodgy battery can include dimming headlights, particularly when the car is idle, along with flickering dashboard lights and even electric windows that roll up slower than they should. Once visible tell, which may not always indicate the death of a car battery but should be assessed regularly, is the presence of corrosion on the battery itself.

If you’re looking to sell a scrap battery, we’ve put together a guide explaining just how much you can expect to sell a battery for – although be prepared it isn’t a particularly high figure.

If your failing battery is one item on a long list of issues (or if you just need some cash in a hurry) then sell your car with Scrap Car Comparison. We’ll find you the best deals in just 30 seconds and thanks to our nationwide network of scrap dealers at trusted, professional Authorised Treatment Facilities, we can even arrange the collection of your car at no extra cost. So, use our online valuation calculator to find out how much your car could be worth – battery or no battery – and sell it today with Scrap Car Comparison.

Get Quote Now

Get Offers For
Your Scrap Car In
Less Than 30 Seconds


Best price in 30 seconds

Your request is processing

Your request is processing...