Glossary
BCI group size
A standard code, like group 24, 27 or 31, describing a battery's physical dimensions and terminal layout only.
BCI group size is a Battery Council International standard that tells you the physical box dimensions and terminal placement of a battery, nothing more. Group 24, 27, and 31 are the sizes most common in RV battery compartments, and matching the group size is what lets a replacement battery fit the existing tray and hold-down hardware.
Group size says nothing about amp-hour capacity, chemistry, or how the battery performs. Two batteries in the same group size can have noticeably different capacity depending on whether they are flooded lead-acid, AGM, or lithium, since lithium cells pack more usable energy into the same case.
A frequent confusion is assuming a bigger group number automatically means more power, or shopping only by group size and skipping the amp-hour rating entirely. Before buying, measure the existing battery compartment and check both the group size for physical fit and the amp-hour and chemistry for actual performance.
Where this comes up
- Best RV BatteriesBuying guide
- RV Battery Group Size ChartArticle