Understanding the battery basics

A car battery has a shelf life of anywhere between 3 to 5 years. Many come with a guarantee, so be sure to check your original purchase or dealership receipt to find out if you’ll have to pay for a replacement or if your faulty or failing battery is covered.

So: “Which battery for my car?” It’s a common question. When choosing a new battery, there are hundreds of different sizes and brands to pick between. A lengthier guarantee or well-known brand are often sensible options to help with your decision.

Prices will vary too, and with a new battery, picking the cheapest one available can be asking for trouble.

Finding your battery type by registration

There are hundreds of online car battery finder pages. All you have to do is type in your registration number, and you’ll see the correct group code or a selection of different batteries that are suitable for your vehicle. You should be able to determine the size and power if you’re planning on using the information to shop around for the best deal.

With so many online databases available, it’s easy to track down the correct type of car battery by reg.

Choosing the correct battery – fitting criteria

  1. Battery group codes – the correct battery group codes are in your owner’s handbook, or if replacing like-for-like, should be available on your existing battery.
  2. Determine the dimensions – Measurements are in mm and are LxWxH.
  3. Consider the terminal layout – Looking at the front of the battery, its terminals could be at the front or the rear of the battery with the positive terminal at the right or left-hand side.
  4. Decide the terminal type – There are 4 types of terminal; each will correspond with your battery connectors:
    1. Standard UK post – are the most common
    2. Japanese post – have a narrower negative post than the positive
    3. Lug terminals –are square posts with a bolt-through hole
    4. Side terminals – just as the name suggests, these are located on the side of the battery

Battery power

Battery power is determined by two settings: its cold cranking amps (CCA) and its reserve capacity (RC).

Cold cranking amps (CCA)

This rating lets drivers know how well the battery starts the car in cold conditions. Starting your car and your battery’s performance is hindered in cold-weather situations. This figure is the number of amps your 12-volt battery can deliver at 0°F for 30 seconds, maintaining a voltage of 7.2v.

If the CCA figure is significantly higher than recommended by your vehicle manufacturer, it isn’t always the best battery for the job. If you can’t match the CCA exactly, one slightly higher is preferable to one marginally lower.

Don’t confuse a battery’s CCA with its CA (cranking amps). The cranking amps measure is taken at 32°F instead of zero, so provides a higher count.

Reserve capacity (RC)

Your battery’s reserve capacity is the time a fully charged new battery will operate if the alternator fails. Usually, it’s the vehicle’s alternator that converts power from the engine into the electricity it uses to keep the car moving.

If you’re looking for the numbers behind the science, this is how long the battery will deliver 25 amps at 80°F without falling below the car’s required minimum voltage.

C20 capacity

Not all batteries will display this, but those that do, indicate how much energy is stored in the battery. The C20 capacity is measured in ampere-hours (Ah).

What size battery do I need?

There are a few factors to consider for choosing a new battery or battery replacement. Just because your battery will fit comfortably in its holding tray, doesn’t necessarily mean it’s the right one for your car.

  • Location of terminals
  • Type of terminals
  • Number of cells
  • Voltage
  • Cold cranking amperage

However, the main factor of whether or not your replacement battery will fit in your car is size.

Battery group sizes

Each battery has a specific code or group size. If you enter your registration number into one of the online battery finders, you’ll notice that each battery has a corresponding group size. The group size of your battery can also be found in your owners’ handbook.

The group size is generally a 3 number code. Some codes are followed by a letter, or combination of letters.

What type of battery is best?

You can pick from a handful of different types of battery—some better than others. If you’re asking “What battery for my car?” then the following explanation will show you which are your premium options and why.

Lead acid

The lead acid battery is the most common type of battery on the market today. It’s the battery your car came with (if you own a typical family petrol or diesel car). In general, a lead acid battery will provide around 20,000 starts.


Calcium batteries are a little higher quality. They’ve got around 18% more starting power and should operate more efficiently on those cold morning starts. A calcium battery will provide you with approximately 30,000 starts.

Silver calcium

A silver calcium battery is a top-end option. They will usually supply around 33% more power than the traditional lead acid option, and provide about 50,000 starts. Motorists heavily dependent on additional and advanced electrical components operating their vehicle—or plugged in to it—should consider this type of battery.

Advanced flooded battery (AFB)

An advanced flooded battery is an advanced battery option designed especially with stop/start motoring in mind. Also known as EFB or ECM batteries, they provide as many as 360,000 starts.

Absorbent Glass Mat (AGM)

AGM batteries are a super heavy-duty option. These batteries aren’t interchangeable with AFB or ECM batteries. Changing an AGM battery will mean specialist software reconfiguration, so this isn’t a job for the home DIY mechanic.

Let Fixter find your premium replacement

Whatever car you drive, Fixter can help you find the ideal battery replacement service for it. With our contactless collection and delivery service, we’ll also save you time and money.

Why not take a look right now to see the excellent prices and parts Fixter have to offer?

If you’re not sure whether your battery is on its last legs or whether there’s an issue with your car’s electrics, our expert partners are ready and waiting to check it out, offering you the best advice available.

We’ll also make sure your old battery is recycled in the correct way. You should never just throw a car battery away with your household rubbish, as they contain many harmful materials.

About Fixter

Fixter is revolutionising the car maintenance industry, one repair at a time. Fixter was founded to make car maintenance as easy as booking a taxi. Digital, transparent and stress-free, with world-class customer service. Since launching in Manchester in 2017, Fixter has expanded to more than 100 cities across the UK and provided thousands of car owners with honest, convenient and affordable car repair services.