Group 42 Battery [Uses, Size, and Replacements]

Looking for a BCI group 42 battery for your classic VW, BMW, or Porsche?

Well, you’re in the right place. Before you go ahead purchasing and installing a new battery take the time to double check you’re getting it right.

These products can be confusing if you’re not 100% sure about what you need. For example, do you need AGM or flooded? Will it fit in your battery compartment?

Below you’ll find detailed information, dimensions, chemistry types, and uses for a group 42 battery. Plus there’s answers to your biggest questions.

What is a Group 42 Battery?

BCI group 42 batteries are predominantly built for starting small to medium sized cars. These mid-sized batteries are only now found in older vehicles produced prior to 2000.

As they are made for engine cranking they produce a respectable 500CCA which is enough to start smaller petrol engines.

They were common with German automobile manufacturers like Volkswagen, BMW, and Audi. In addition to this, US car brands like Ford are known to have used this group.

If you’re looking for a group 42 battery you probably have a classic car like a VW Bug or a Porsche 914.

The good news is you can still buy these 12V starting batteries for your vehicle from specialist online retailers. Plus there are equivalent replacements like Group 58R with similar dimensions and performance.

Manufacturers don’t produce group 42 as deep cycle or marine batteries.

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BCI Group 42 Dimensions and Weight

The dimensions of a group 42 battery are:

• Length: 9 5/16 inches (243mm)
• Height: 6 13/16 inches (173mm)
• Width: 6 13/16 inches (173mm)
• Average Weight: 30lbs (13kg)
• Terminal Type: SAE Automotive

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Chemistry Type and Application

The majority of group 42 batteries are built as traditional flooded lead acid (WET). These provide reliable performance but require maintenance and careful installation. You’ll need to top up the electrolyte battery acid solution every few months. You can easily do this yourself or ask a local garage. Adding to this, make sure to always wear gloves when handling the equipment.

It is rare to find a sealed lead acid group 42 battery, but not impossible.

If you’re looking for an AGM option then Odyssey makes one. Make sure your vehicle is prepared to correctly charge AGM batteries as overcharging is an issue that quickly causes damage. On the plus side, they are more reliable and offer longer lasting performance.

The application of these batteries is restricted for starting / cranking. Battery makers don’t bother producing deep cycle or marine options as there is no demand. Adding to this, you won’t find any lithium equivalents either.

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Pros and Cons of Group 42 Batteries

Let’s look at the advantages and disadvantages of these batteries. 

Pros:

• Used in classic VW and Porsche cars
• Relatively small and lighter in weight
• Available from online retailers
• WET and AGM options available

Cons:

• Becoming less common
• Not used in modern vehicles
• No deep cycle or marine

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Group 42 vs Group 58R Batteries

Group 58R and group 42 are seen as equivalent replacements for one another. In particular, you can use a group 42 as a group 58R.

In fact, many retailers mark these products as both. You might see it written as ‘Group 42/58R.’ The dimensions of the two batteries are close and they both provide around 500CCA.

You still need to be careful and double check the dimensions of your battery compartments. As you see on the table below, a group 58R is longer, wider, and taller. So it might be a tight squeeze. On the other hand, you could easily fit a 42 in place of a 58R as it is slightly smaller.

Group	Length (inch)	Width (inch)	Height (inch)
58R	10 1/16	7 3/16	6 15/16
42	9 5/16	6 13/16	6 13/16

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Group 42 vs Group 90 Batteries

If you’re looking for a group 42 equivalent replacement then consider a group 90. 

It has similar physical dimensions, although it is a little larger. In my experience, you should be able to squeeze it into your battery compartment but double check your measurements. As you can see in the comparison below it’s close!

One benefit of group 90 is a higher 600+CCA. This won’t cause any issues, in fact it gives you a slightly faster start and less wear on the starter motor. Additionally, 

Group	Length(inch)	Width(inch)	Height(inch)
90	9 11/16	7 3/16	6 15/16
42	9 5/16	6 13/16	6 13/16

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Replacing a Group 42 Battery in a VW Bug

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FAQ

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Summary

I hope this page about BCI group 42 batteries helps clear up any of your questions.

As you have discovered, they are produced as a starting battery for cranking small and older car engines. 

They’re commonly seen in classic VW Beetles, Porsche 914, and BMW 2002. That’s a badass selection of cars!

It’s a relatively small battery which means it’s not too heavy but only delivers 500CCA which is not enough for many modern vehicles.

If you’re looking for equivalents then take a look at Group 58R and 90.