Automotive Reference
The BCI group number is really three things: the case dimensions, the terminal type, and which post is positive. Get all three right and the battery fits and connects.
"Group 48" isn't a capacity — it's a physical spec. Same group = same box size and the positive terminal in the same place, so it drops in and the cables reach.
Dimensions are the BCI standard (L × W × H). "R" suffix means the positive terminal is on the opposite side.
| Group | L × W × H (in) | L × W × H (mm) | Common on |
|---|---|---|---|
| 24 / 24F | 10.3 × 6.8 × 8.9 | 260 × 173 × 225 | Older import cars, marine |
| 34 / 78 | 10.3 × 6.8 × 7.9 | 260 × 173 × 200 | GM trucks & cars |
| 35 | 9.1 × 6.9 × 8.9 | 230 × 175 × 225 | Japanese cars/SUVs |
| 47 (H5) | 9.7 × 6.9 × 7.5 | 246 × 175 × 190 | Many European/US compacts |
| 48 (H6) | 12.1 × 6.9 × 7.5 | 306 × 175 × 190 | European & US mid-size |
| 49 (H8) | 15.0 × 6.9 × 7.5 | 381 × 175 × 190 | Larger European/luxury |
| 51R | 9.4 × 5.1 × 8.8 | 238 × 129 × 223 | Honda, Nissan compacts |
| 65 | 12.1 × 7.5 × 7.6 | 306 × 190 × 192 | Ford trucks/SUVs |
It's a physical standard set by the BCI (Battery Council International): the case dimensions, terminal type (top or side post) and which side is positive. It is not the capacity — two batteries of the same group can have different cranking amps.
Only if it fits the tray and hold-down and the terminals line up with your cables. A larger group often won't fit; a smaller one may not secure or crank enough. Stick to the group your vehicle specifies unless you've confirmed the alternative physically fits and connects.
It marks terminal position. "R" (reverse) means the positive post is on the opposite side from the standard group; "F" is a front-terminal variant. Get this wrong and the cables won't reach — the case fits but you can't hook it up.
It's printed on the label of your current battery, and listed in the owner's manual. If the label's gone, measure the case (L×W×H) and match it to the chart above, then confirm the terminal layout.