BCI group size chart: what fits the tray
Group size is a physical envelope, not a performance rating. Two batteries of the same group size can have wildly different amp-hour and CCA figures. Get the group wrong and the battery does not fit; get the spec wrong and it fits but disappoints.
| Group | Approx. L × W × H (in) | Common use | Typical Ah | Typical CCA |
|---|---|---|---|---|
| 24 / 24F | 10.25 × 6.8 × 8.9 | Many Asian and older US cars, some marine | 60-80 | 500-700 |
| 27 / 27F | 12.1 × 6.8 × 8.9 | Trucks, marine starting, older diesels | 80-110 | 600-900 |
| 31 | 13.0 × 6.8 × 9.4 | Marine house, RV, commercial | 95-125 | 800-1,100 |
| 34 / 34R | 10.25 × 6.8 × 7.9 | Many European cars (check terminal side) | 50-70 | 600-800 |
| 35 | 9.1 × 6.9 × 8.9 | Japanese cars, compact | 45-60 | 450-650 |
| 65 | 12.1 × 7.5 × 7.5 | Ford/Chrysler group, common upgrade | 70-85 | 700-900 |
| GC2 (golf) | 10.3 × 7.1 × 11.1 | 6V deep cycle, golf carts, RV house | 200-230 (6V) | n/a |
| 8V GC8 | 10.3 × 7.1 × 10.9 | 48V golf cart packs | 150-170 (8V) | n/a |
Figures are nominal and vary by manufacturer — always check the published dimensions and terminal orientation for the exact model. The letter "F" or "R" indicates terminal layout (positive post position), which matters as much as physical size: a 24F will physically fit where a 24 is specified but the cables may not reach.
How to confirm your group size
Read the label on the existing battery; if it is illegible, measure the tray's length, width and height and match against the table, then confirm the terminal positions against your cables. Post types matter too: SAE posts, stud terminals, or both. For marine and RV, ensure the case is rated for the vibration and, if it lives indoors, that it is sealed.