Battery groups › 21
BCI battery group
Group 21 battery size
A BCI group 21 battery is at most 208 mm long, 173 mm wide and 222 mm tall (8.19 × 6.81 × 8.74 in), according to the Battery Council International group chart.
| Maximum size | 208 × 173 × 222 mm |
|---|---|
| In inches | 8.19 × 6.81 × 8.74 |
| Terminal types | A and A2 |
| Polarity | Standard layout for this group |
| Cold cranking amps (OE range) | 305–420 A |
| JIS equivalents | 50D20R (BCI best fit) |
Cars whose manuals point to group 21
None of the owner's manuals this site has read so far print group 21. 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 21
To take a group 21, the tray needs at least 208 mm (8.19 in) of length and 173 mm (6.81 in) of width inside the hold-down, and 222 mm (8.74 in) of height below the hood or any bracket, with room left for the cable ends. These are BCI maximums: a real group 21 battery can be a few millimetres smaller, never larger. Original-equipment batteries in this group were rated from 305 to 420 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 21 |
|---|---|---|
| 21R | 208 × 173 × 222 | 0 mm length, 0 mm width, 0 mm height |
| 121R | 208 × 177 × 215 | 0 mm length, +4 mm width, -7 mm height |
| 71 | 208 × 179 × 216 | 0 mm length, +6 mm width, -6 mm height |
| 26 | 208 × 173 × 197 | 0 mm length, 0 mm width, -25 mm height |
| 26R | 208 × 173 × 197 | 0 mm length, 0 mm width, -25 mm height |
Positive numbers mean the other group is bigger than group 21. 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 21
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 6. Checked 2026-10-20.