Battery groups › 121R
BCI battery group
Group 121R battery size
A BCI group 121R battery is at most 208 mm long, 177 mm wide and 215 mm tall (8.19 × 6.97 × 8.46 in), according to the Battery Council International group chart.
| Maximum size | 208 × 177 × 215 mm |
|---|---|
| In inches | 8.19 × 6.97 × 8.46 |
| Terminal types | A |
| Polarity | Reversed (R): positive terminal on the opposite side from the base group |
| Cold cranking amps (OE range) | 410–600 A |
Cars whose manuals point to group 121R
None of the owner's manuals this site has read so far print group 121R. Most Japanese and Korean makers print a case size or capacity instead of a BCI group, so the battery label on the car is the better guide.
Measuring for a group 121R
To take a group 121R, the tray needs at least 208 mm (8.19 in) of length and 177 mm (6.97 in) of width inside the hold-down, and 215 mm (8.46 in) of height below the hood or any bracket, with room left for the cable ends. These are BCI maximums: a real group 121R battery can be a few millimetres smaller, never larger. Original-equipment batteries in this group were rated from 410 to 600 cold cranking amps, so the right rating depends on the car; match or exceed the rating on the battery you are replacing.
Nearby sizes
| Group | L × W × H (mm) | Difference from 121R |
|---|---|---|
| 71 | 208 × 179 × 216 | 0 mm length, +2 mm width, +1 mm height |
| 21 | 208 × 173 × 222 | 0 mm length, -4 mm width, +7 mm height |
| 21R | 208 × 173 × 222 | 0 mm length, -4 mm width, +7 mm height |
| 26 | 208 × 173 × 197 | 0 mm length, -4 mm width, -18 mm height |
| 26R | 208 × 173 × 197 | 0 mm length, -4 mm width, -18 mm height |
Positive numbers mean the other group is bigger than group 121R. A bigger case only fits if your tray and hold-down have that much spare room; measure inside the hold-down frame, not the old battery.
Fitting a group 121R
The group sets the case size, terminal position and hold-down. A battery from another group can only replace it when the length, width and height all fit the tray and the terminals land on the same sides. No other passenger-car group in the BCI chart has exactly the same case size and polarity. Use the tray fit checker to list every group that fits a measured space.
Source: Battery Council International, BCI Group Sizes (Oct 2023 PDF), page 7. Checked 2026-10-20.