What Do Battery Groups Mean?
We all know batteries come in various shapes and sizes, but what does it mean when someone says a battery "group?" The simple answer is that in the world of car batteries, group means size. If that were also the case in the world of shoes, you would ask someone at Footlocker for a Group 11 Vans Old Skool. So why don't battery people just identify batteries by "sizes" rather than "groups?" Probably for the same reason a Group 34 battery is smaller than a Group 27 battery, but larger than a Group 51 battery- we like to confuse people with industry jargon.
There are a couple of different organizations that come up with these sizes/groups, including the BCI (which stands for Battery Council International, instead of the IBC) and many of their common sizes include the previously-mentioned Group 34 & 27, as well as the 31 and 35. JIS (which stands for Japanese Industrial Standard) groups include the 32C24R, 46B24R and 95E41R, among others. There's also DIN (which stands for Deutsches Institut für Normung aka German Industrial Standard) groups, like the H6, H7 and H8 batteries.
So does that mean that all German cars have DIN sizes and all American cars have BCI sizes? Again, because the battery industry likes to be confusing, the answer is "not necessarily." For example, the DIN group (battery size) for a 2016 Mini Cooper is an H6. However, the BCI refers to that exact same battery as a "Group 48" battery. To complicate it even further, many brands and retailers will add additional characters to those designations, turning a Group 48/H6 battery into a DH6 or an MTP-48/H6.
Fortunately, the one thing the battery industry has generally done to alleviate at least some of this confusion, is to create fitment guides, that can tell you which group (or sizes, because some vehicles can use multiple battery sizes). If you know the year, make, model and engine size of your vehicle, there's probably a booklet at an auto parts store or an online battery fitment guide you can access with your phone, that will tell you which batteries will work in your vehicle.