Car battery group size explained

Need a new battery for your vehicle but not sure what size to get? Picking the wrong one can prevent you from reaching your destination and even damage your car. Battery group size ratings can help you find the perfect fit so you can take the guesswork out of this important selection.

Let’s go over what car battery group sizes mean, how they’re defined, and how to choose the right one for your needs.

What a battery group size is

When you’re browsing for a battery, you’ll notice a series of numbers and letters in each one’s name. These figures represent the battery group size. Because these values have become standardized internationally, you can also use them to find a battery for your imported vehicle.

Batteries are placed into groups based on their voltage, maximum dimensions, terminal placement, internal chemistry, and any special features that may affect the way the battery fits in your vehicle. Group size ratings are available for passenger cars, trucks, ATVs, motorcycles, jet skis, industrial equipment, and more.

In North America, the Battery Council International (BCI) sets and publishes car battery group sizes. The BCI is a trade association that includes manufacturers, recyclers, distributors, and retailer organizations that supply original and aftermarket batteries. It also controls the standard size, weight, and testing procedures for all batteries sold in Canada and the United States.

Battery manufacturers use BCI ratings as a template to inform the design of their products. To succeed in the aftermarket, manufacturers and automakers collaborate to ensure the batteries will work with the vehicles available.

How group sizes are set

Battery group sizes are primarily determined by four characteristics:

  1. Battery dimensions: batteries within the same group are all the same physical size (i.e., length, width, height). This ensures a proper fit in your vehicle.
  2. Performance: cold cranking amperage (CCA) or amp hours are measured comparatively to the age of the vehicle. If you choose a battery whose CCA or amp hours rating is too low, your vehicle won’t start.
  3. Terminal position: options are side post batteries, recessed top post batteries, or standard top post batteries. Matching this value will ensure you can safely attach your cables.
  4. Chemistry: batteries can be lead chemistry with flooded technology, enhanced flooded battery, absorbed glass mat, or lithium-ion. Some vehicles can accept one or more of these types. However, others require a specific type.

To promote universality, BCI ratings align with other international battery standards.

Battery group size examples

Based on the criteria outlined above, a battery group size will be given a specific number. All batteries with the same figures (i.e., dimensions, terminal placement, etc.) will fall into the same grouping.

Some of the most popular battery group sizes for passenger vehicles include 24, 27, 34, 35, 49, 65, and 78. RVs and boats often use the same group size as passenger cars for their batteries.

Sample group sizes

The sample sizes below are all for 12-volt passenger and light commercial vehicle batteries.

Group 24

  • L x W x H (cm): 26 x 17.3 x 22.5
  • Terminals: A, A2
  • Assembly figure: 10
  • CCA at 0 °C: 200-1000

Group 34

  • L x W x H (cm): 26 x 17.3 x 20
  • Terminals: A
  • Assembly figure: 10
  • CCA at 0 °C: 235-1000

Group 78

  • L x W x H (cm): 26 x 17.9 x 19.6
  • Terminals: S
  • Assembly figure: 17
  • CCA at 0 °C: 465-875

Keep in mind, a higher group size doesn’t necessarily mean a bigger battery.

Selecting a battery

To pick the right battery group size, you need to know what size battery tray your vehicle has. Getting a snug fit will ensure the battery works properly and avoid potential damage to your vehicle. Also, double-check the terminal position and CCA rating before purchasing.

Your owner’s manual will provide the ideal battery group size for your vehicle. If you don’t have the physical copy, you can find a digital version or use your current battery size as a reference.

Some vehicles may be able to handle a larger battery than what they were originally installed with. For more advice on making this switch, visit a NAPA Auto Parts store to speak with an expert. You can also find a wide selection of batteries available in NAPA stores and online at NAPACanada.com.

Once you have your new battery picked out, you can get it professionally replaced at a NAPA AUTOPRO service centre or do it yourself by following this guide.

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