Group 121R battery size

Close in size

Groups within 10 mm (0.4 in) on every side:

• Group 21: 8.19 x 6.81 x 8.74 in, different terminal layout (BCI figure 10, not 11H).
• Group 21R: 8.19 x 6.81 x 8.74 in, different terminal layout (BCI figure 11, not 11H).

Before you buy a group 121R battery

• Read the group number on the label of the battery in your car, or in the owner's manual: it should say 121R.
• The "R" means the terminals are reversed compared with the same number without R: the positive post is on the other side.
• Choose cold cranking amps (CCA) at least as high as the original, especially for cold winters.
• Measure your battery tray and the room above it, then compare with the size printed for the exact battery you pick, not only with the group number.
• Group 121R has top posts: the new battery must match, and the hold-down must fit the box.
• Most stores take the old battery back for recycling, often against a core charge.

Good to know about group 121R

• Retailers' specifications list the positive terminal of a group 121R battery on the right.^1,2,3
• Group 121R is listed for some Hyundai models, such as the Elantra, and some Kia models, such as the Forte.^4,5,6
• Batteries Plus and East Penn list a group 121R at 8.25 in long and Continental at 8.12 in, within 2 mm of the 8.19 in BCI figure; all three list a height of 8.13 in or less, under the 8.46 in BCI maximum.^7,8,9

How we checked this page

Checked on October 16, 2026. We kept a fact only when two independent sources agree, and each one is numbered to its sources below. We never write a price: the listings come straight from eBay and show what sellers ask. This page was written with an AI assistant and checked against the sources below.