Battery Group Size Explained: What the Code Describes

Short answer: with battery group size explained in one line, the code is mainly a shape. It is a standard from Battery Council International (BCI) that fixes a battery's maximum case dimensions, where its terminals sit, which way round they are, and the terminal style. A Group 48 and a Group 24F are different boxes, not different strengths. The group number tells you very little about power. BCI's own chart lists original-equipment cold cranking amps for a single group across a very wide range, so CCA, reserve capacity and chemistry have to be checked separately.

Figures in this article come from BCI's published group size chart and its group sizes page, both read 2026-09-24. They describe the standard, not what your car needs. Your own vehicle's number comes from its documentation or the battery it left the factory with.

What BCI says a group size is

BCI's group sizes page (read 2026-09-24) says batteries "are classified into numbered group sizes according to their voltage, maximum overall dimensions, terminal arrangement, and special features that may affect battery fit."

It then names four characteristics. The first is dimensions, and BCI says batteries within a group "must be the same physical size (i.e., within 2mm) in order to ensure the proper fitment in a vehicle." The second is performance, measured "through cold cranking amps or amp hours" depending on the age of the vehicle. The third is terminal position, "which ensures a vehicle's electrical cables properly align to the battery." The fourth is chemistry: BCI assumes flooded lead-acid by default and assigns designations for EFB and AGM variants.

So performance is part of the definition. But look at how BCI's own chart treats it, and the group number turns out to say much more about the box than about what is inside.

Why the number is a shape, not a strength

BCI's group size chart (PDF, read 2026-09-24) lists every group with its maximum dimensions, terminal type, an assembly figure number and an "O.E. Performance Range" that it marks "for Reference Only."

For Group 24, that reference range for cold cranking performance runs from 200 to 1000 amps. For Group 48 it runs from 315 to 850. Two batteries can share a group, fit the same tray and connect to the same cables while differing several times over in cranking performance. That is why "same group" never means "same battery."

The number is not a size scale either. It is a label. In BCI's chart, Group 49 is 353 mm long and Group 51 is 238 mm long, so the higher number is the much shorter case.

Battery group size explained, suffix by suffix

The letters after a group number are where many wrong purchases happen, because they look like minor variations. In BCI's chart, each one changes something physical. Here is the Group 24 family, straight from BCI's table.

A 24R has almost the same box as a 24, but BCI draws its terminals the other way round. If your cables are cut for one layout, the other will not reach, or will reach only by stretching a cable across the case. A 24F is 13 mm longer than a 24 in BCI's table, which can decide whether the hold-down clamp closes.

This answers the question behind the "Group 48 or Group 24F" confusion. BCI lists Group 48 at 278 x 175 x 190 mm and Group 24F at 273 x 173 x 229 mm. They are close in length and width, but the 24F is 39 mm taller, and the two use different assembly figures. It is a shape question first.

The European and Japanese codes on the same label

Many batteries carry a second code beside the BCI group, and BCI's chart cross-references them.

• DIN and EN codes. BCI's reference chart pairs Group 48 with DIN code H6 and EN code LN3, Group 47 with H5 and LN2, Group 49 with H8 and LN5, and Group 94R with H7 and LN4. That is why you see labels such as "48/H6."
• Reversed versions with new numbers. BCI notes that Group 148 "is equivalent to a reversed termination 48 (H6)." The reversal is written as a different number, not a letter.
• JIS codes. BCI's key for a code such as S65D26R reads: S for a valve-regulated original battery, 65 a performance ranking, D a class of width and height, 26 an approximate length that you multiply by 10 to get millimeters, and a last letter for polarity.

BCI calls these cross-references its "best fit estimate" and disclaims their accuracy. Treat a DIN or JIS equivalent as a lead to check against the dimensions, not as a guarantee. Our car battery group size chart lists the maximum dimensions for all 90 passenger car groups side by side.

Terminals and hold-downs: the parts of fit people forget

A group size also implies a terminal style, and BCI's chart names the types. Type A is the SAE top post, Type A1 the DIN post, Type A2 the EN/JIS post, Type A3 the JIS pencil post, and Type S the side terminal. They are not interchangeable by eye. On its JIS chart, BCI notes that an original post "may be small diameter JIS size" and that a "connector change may be required."

Many European-style cases are held down by a ledge along the bottom of the case rather than a bar across the top. BCI's reference chart names three common ledge types: B1 and B3 at 10.5 mm high, and B4 at 19.0 mm high, with different notch patterns. It adds that "others may be used." A battery with the right footprint and the wrong ledge may not lock into the tray clamp.

What the group size does not tell you

This is the part the retailer lookups tend to skip, because their job ends at "this one fits."

• Cranking performance and reserve. CCA, reserve capacity and amp-hours are separate ratings on the label. BCI's own ranges show how far they vary within one group.
• Chemistry. BCI treats flooded, EFB and AGM as distinct designations. Whether a car built with one can take another is a separate question, and your owner's manual is the authority on it.
• Venting. Some original batteries are designed to vent through a tube, which matters when the battery sits in the trunk or cabin. BCI's JIS chart flags some original batteries as "Remote Venting" designs. A battery that fits the tray but lacks the vent connection is not a match for that location.
• Setup after fitting. Some vehicles need a step after a battery change so the car's systems know a new battery is fitted. The group size cannot tell you whether yours does.
• Condition. The group code on your old battery says what was fitted, not whether that battery or the charging system is healthy. Testing either one is a job for a shop.

Where your car's group size actually lives

Work from the most reliable source down.

1. The owner's manual. Many list the battery specification, sometimes with the group size. If yours is missing, free owner's manuals by manufacturer shows where to get one.
2. The battery the car was built with. The label on the original battery is strong evidence. A replacement fitted by a previous owner is only evidence of what someone bought, which may not be what the car was specified for.
3. BCI's application data. BCI's group sizes page says it also issues a vehicle replacement database covering "over 160,000 vehicles from over 85 years." Retailer lookups draw on application data of this kind.
4. The tray, cables and hold-down. If sources disagree, the physical space, cable reach, terminal side and hold-down type settle what will fit, even if they cannot settle what performance the car needs.

When two lookups give two different group numbers, it is usually a data difference rather than a trick. Why two websites give your car two different numbers explains how that happens, and where to find vehicle specs ranks the sources.

If you lift out the old battery to read its label, follow your manual's procedure. Wear eye protection, work somewhere ventilated, and keep tools away from the terminals.

Frequently asked questions

Does a battery group size tell me how powerful the battery is?

Not usefully. BCI lists performance among the characteristics of a group, but its chart shows original-equipment cold cranking amps for a single group across a very wide range. Check the CCA, reserve capacity and chemistry on the label against your manual. For a worked equipment example, our John Deere battery size chart matches Deere mowers, Gators and tractors to their BCI groups. Our Kubota tractor battery size chart does the same for Kubota, decoding the JIS battery types Kubota prints in its manuals.

What does the R mean in a battery group size like 24R?

In BCI's chart, the R version puts the positive and negative posts on opposite ends from the standard group, on nearly the same box. If the cables are cut for one layout, the other may not fit.

Is Group 24F the same as Group 24?

No. BCI lists Group 24F as a longer, slightly taller case with a different assembly figure. The letter changes the physical fit.

What does H6 or 48/H6 mean on a battery?

H6 is the DIN code that BCI's reference chart pairs with Group 48, which is why many labels print both. BCI describes these pairings as a best fit estimate, so confirm the dimensions and terminal layout.

Can I fit a different group size if it fits the tray?

A different group can fit the tray and still differ in terminal side, post type, height under the hood or hold-down ledge. Check each of those, then confirm the performance ratings and chemistry your manual calls for.