RV Battery Group Size Chart
BCI (Battery Council International) group sizes standardize a battery's physical dimensions and terminal layout across brands, not its chemistry or capacity, so a group 27 battery from any manufacturer fits a group 27 tray, but two group 27 batteries can still have meaningfully different amp-hour ratings. This chart lists the dimensions and typical capacity range for the three group sizes most common in RVs.
Dimensions and capacity by group size
Group 24: approximately 10.25 x 6.81 x 8.88 inches (26 x 17.3 x 22.5cm), typical capacity 70-85 amp-hours. The smallest and lightest of the three common RV sizes, often used where space is tight or as a secondary battery.
Group 27: approximately 12.06 x 6.81 x 8.88 inches (30.6 x 17.3 x 22.5cm), typical capacity 85-105 amp-hours. Longer than a group 24 at the same width and height, giving noticeably more capacity in a similar footprint otherwise.
Group 31: approximately 13.00 x 6.81 x 9.44 inches (33 x 17.3 x 24cm), typical capacity 95-125 amp-hours. The largest of the three, offering the most capacity but demanding the most tray space and weight capacity.
Length is usually the limiting factor, not width
All three group sizes share nearly identical width (6.81 inches), so the practical question when upgrading is almost always whether your battery tray and hold-down have enough length and height clearance, not width. Measure your existing tray's internal length before assuming a larger group size will fit, since jumping from a 24 to a 27 or 31 adds two to three inches of length that many factory-installed trays were not built to accommodate.
Weight also increases meaningfully with group size, particularly for lead-acid chemistries, so confirm your battery compartment's structural mounting and any weight rating limits before upgrading to a larger group size, especially in a factory tray designed around the smaller original battery.
Group size does not tell you the chemistry or true capacity
A group size describes the shell dimensions and terminal layout only, so lead-acid, AGM, and lithium (LiFePO4) batteries all come in the same group sizes despite very different weights, usable capacities, and prices. A lithium battery in a given group size typically weighs significantly less and delivers more usable capacity than a lead-acid battery of the same physical group size, since lead-acid batteries should not be discharged as deeply without shortening their lifespan.
When comparing batteries of the same group size, compare amp-hour rating and chemistry directly rather than assuming size alone tells you capacity, since two groups-27 batteries from different manufacturers and chemistries can differ in real usable power by a wide margin despite fitting the identical tray.