Keeping on top of batteries

  • 2,468

With all this cold weather, is your car struggling or failing to start? Think you need a new battery? Here's what to look for and how to replace it.

Before you replace a suspected flat battery, you need to make sure it's actually the battery that's at fault. If you've left the lights on, or some other electrical item, and know that's what's caused the issue, you may be able to get away with either jump starting the car, or charging the battery back up with a battery charger.

If, however, it has gradually been getting worse, and in particular struggling to start the car when the weather is cold, then it's likely the battery is dead.

Handy parts and tools

Test it

If you want to be certain you can buy a cheap multi-meter and test the voltage. With the engine off and the car sitting for some time the battery should register 12.6v.

Any lower and it suggests either the battery’s in need of replacement or the car's charging system is at fault. With the engine running you need to see a voltage of between 13.8-14.4V. Anywhere outside of that range and further investigation is needed.

Handy parts and tools

Buying a New Battery

If you do decide it's the battery – replacement is generally straightforward. You can replace like-with-like, although you can get away with a battery that is larger than the original one if there is sufficient space available. If your car is fitted with a 'stop-start' system, then it needs a battery suitable for that application, and should be

Never fit a smaller battery than is currently fitted. You also need to ensure that your replacement battery has the same terminals. Most have cylindrical metal posts. Also make sure the terminals (the + and – posts) are in the same place on the one you're considering buying.

Batteries are sold in standard sizes, but also with different rating for Ah (Amp hours) and CCA (Cold Cranking Amps).

Ah refers to the length of time the battery can deliver a continuous specified current – in simple terms with the engine switched off a 70Ah battery would power your head unit for longer than a 60Ah battery. CCA refers to amount of amps the battery can deliver at -17C for 30 seconds without dropping below 7.2v.

Which basically means that the more CCAs the better the car will start in very cold temperatures. You can specify batteries with more Ah and CCAs than the standard battery if you wish, (some people fit the diesel equivalent battery on their petrol cars, because they have a higher CCA rating) and it will do no harm, but it's not strictly necessary.

It's unwise to fit a battery with lower 'ratings’, as you could quickly find it ceases to become effective.

To find what battery you have either look at the battery itself, check your handbook, or look at one of the many online sites where you input your car's details. It will usually be referred to with a three-digit number such as 068, or 075 etc – and once armed with that information you can decide which battery to buy, and how many AH and CCAs to go for!

Replacing the Battery

If you can access the battery, then replacement is usually straightforward:

  • Before you disconnect anything, make sure you know the head unit's security code (if it has one) - disconnecting the battery will mean you've got to input the code to get it working again. If you don't have access to the code, or simply don’t want to lose any of the car's settings you can purchase battery memory savers to keep the settings in place as you swap the batteries over.

  • Remove the ‘–‘ negative clamp first and move it out of the way so that it does not touch the battery terminal.

  • Next remove the ‘+’ positive clamp and also keep it out of the way. If there are any other connections, make a note of where they are. If you're using a spanner, take care not to touch the terminals together and never rest it on top of the battery.

  • Remove the clamp holding the battery in place - commonly there is one bolt and a clamp which holds the base in position. Once undone, you can lift it out. Be aware that it will be heavy!

Expert tip

If the leads that go to the battery are covered in white furry stuff, or are dirty/green, give them a clean before refitting to ensure a good electrical connection. The easiest way to clean the terminals is either with a battery terminal cleaner, or with some electrical contact cleaner.

  • Fit the new battery, refit the clamp, and take care again not to touch anything metal on the terminals.

  • Reconnect the + positive lead to the terminal first, then the – negative lead. Give these a wiggle to make sure they're secure.

  • Start the car!

Handy parts and tools

Get Winter Ready

All the car parts and expert advice you need to keep safely on the road. Expert Tips and Advice for Winter