Home FAQ

Can I use a different battery group size?

Yes, you can typically use a different battery group size in your vehicle, as long as the new battery meets the minimum requirements for your car or truck. However, there are some important factors to consider before making the switch.

Understanding Battery Group Sizes

Battery group sizes refer to the physical dimensions and terminal configurations of automotive batteries. Common group sizes include 24, 34, 35, 47, 51, 65, 75, and 78. The group size determines whether a battery will physically fit in your vehicle's battery tray or compartment.

In addition to size, batteries also have different cold cranking amps (CCA) and reserve capacity (RC) ratings that indicate their power output and runtime. Choosing a battery with the right CCA and RC for your vehicle is crucial to ensure proper starting and electrical system performance.

Factors to Consider When Changing Battery Group Size

Physical Fit: Measure the battery tray in your vehicle and compare the dimensions to the new battery to ensure it will physically fit and be properly secured.

Electrical Compatibility: Verify that the new battery has the same or higher CCA and RC ratings as the original to maintain starting and electrical system performance.

Terminal Configuration: Check that the positive and negative terminals on the new battery are in the same location as the original to allow for proper connection.

Warranty: Using a non-OEM battery may void your vehicle's warranty, so check with your manufacturer before making a change.

As long as you select a replacement battery that meets or exceeds the original specifications, you can typically use a different group size without issue. However, it's always best to consult your owner's manual or a professional mechanic to ensure a safe and proper installation.

Can I use a 51 battery instead of 51R?

No, you should not use a 51 battery instead of a 51R. The "R" in 51R stands for "reverse" or "right," meaning the positive terminal is on the right side when viewed from the front, while a standard 51 battery has the positive terminal on the left. A 51 battery will not work because the battery cables are not long enough to reach the terminals in the correct position.
Why a 51 battery won't work

Incorrect terminal position: The 51R battery is specifically designed for vehicles where the positive terminal is on the right side and the negative is on the left. A 51 battery has the terminals reversed.
Cable length: Your car's battery cables are designed to reach the terminals in a specific orientation. Using a 51 battery will put the positive and negative terminals in the wrong positions, making it impossible to connect the cables without forcing them.

What to do instead

Find the correct battery: Purchase a 51R battery to ensure a correct fit.
Check the battery tray: If the 51R battery is a different size than your original battery, you may need to modify or replace the battery tray to ensure it fits securely.

This video explains the difference between 51 and 51R batteries: 15sOPTIMA BatteriesYouTube · Dec 28, 2021
This video shows how to swap a 151R battery with a 51R battery in a Honda Fit: 53sSeb's GarageYouTube · Mar 30, 2025

Can I use a H6 battery instead of a H7?

No, H6 and H7 batteries are not interchangeable by default because the H7 is physically longer than the H6, although they share the same width, height, and voltage. An H7 may fit as a replacement for an H6 only if there is enough extra space in the vehicle's battery tray to accommodate the increased length, and the hold-down system is still able to secure the larger battery.
Key differences

Size: The H7 battery is approximately 1.5 inches longer than the H6 battery.
Capacity: H7 batteries typically have higher cranking amps and reserve capacity compared to H6 batteries.
Applications: H6 batteries are common in smaller cars, while H7 batteries are often found in larger SUVs, trucks, and luxury vehicles with higher electrical demands or start-stop systems.

Important considerations before a swap

Check for space: Measure the battery tray and ensure there is enough room for the longer H7 battery. You may need to remove a spacer that came with the original H6.
Verify hold-down: Confirm that your vehicle's hold-down bracket can securely fasten the larger H7 battery.
Match electrical needs: The H7 is generally a more powerful battery. While it can be a good upgrade if the space permits, make sure the vehicle's electrical system can support it.
Consult your vehicle manual: Always refer to your owner's manual or a professional to ensure you select the correct battery group size for your specific vehicle model.

What happens if you put the wrong group size battery in a car?

Battery specifications
If you use the wrong size battery, this could cause changes in the flow of electrical currents, resulting in power surges that can damage the onboard computers or other components.

Does the group size matter on a battery?

Yes, battery group size matters significantly because it ensures the battery physically fits in the vehicle's compartment and its terminals align correctly with the car's cables. Using the wrong size can lead to poor connections, damage to the electrical system, or safety risks like overheating or electrical fires.
Why group size is important

Proper fit: The correct group size guarantees the battery's physical dimensions, such as length, width, and height, are compatible with the vehicle's battery tray.
Terminal alignment: The group number also dictates the location and type of battery terminals, ensuring they match the vehicle's battery cables and can be securely connected.
Electrical system compatibility: Different vehicles have different electrical demands. The group size is often matched to the vehicle's specific electrical needs, and using an incorrect size can lead to performance issues.
Safety: A proper fit prevents the battery from shifting, which could cause damage or an electrical short. Improperly secured or connected batteries can lead to performance issues or even electrical fires.

What to do when replacing a battery

Consult your vehicle's manual: The manufacturer's manual is the most reliable source for the correct group size for your vehicle.
Use a compatible group number: If you're unsure, use the BCI (Battery Council International) group number to find compatible options from different brands.
Do not guess: Never use a battery that doesn't fit properly or has the wrong terminal placement, even if it seems to have the right power rating, as this can cause significant problems down the line.

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.