BCI Group Size Chart for LiFePO4: Group 24, 27, 31, 4D and 8D Dimensions (and What Fits)

BCI group sizes are how RV owners, boat builders and dealers describe a battery box: “it takes a Group 31” or “two Group 27s”. When you switch to LiFePO4, the group number is still the quickest way to describe the space you have, but it tells you less than many people assume. This guide gives the maximum dimensions for common group sizes from the Battery Council International (BCI) chart, then explains what the number does not cover and how to confirm that a lithium battery will actually fit.

BCI group size chart: common sizes in mm and inches

The figures below are BCI’s maximum overall dimensions (length × width × height), including terminals, from BCI’s published group size chart. A battery sold as a given group may be smaller than these figures, but should not be larger.

BCI group	Max L × W × H (mm)	Max L × W × H (in)	Terminal types listed	Typical uses
U1	197 × 132 × 186	7 3/4 × 5 3/16 × 7 5/16	X	Garden tractors, mobility, small solar
24	260 × 173 × 225	10 1/4 × 6 13/16 × 8 7/8	A, A2	RV house, marine, trolling motors
24F	273 × 173 × 229	10 3/4 × 6 13/16 × 9	A, A2	Automotive
27	306 × 173 × 225	12 1/16 × 6 13/16 × 8 7/8	A, A2	RV house, marine
27F	318 × 173 × 227	12 1/2 × 6 13/16 × 8 15/16	A, A2	Automotive
31A	330 × 173 × 240	13 × 6 13/16 × 9 7/16	A, M, M1	Marine, RV, commercial vehicles
31T	330 × 173 × 240	13 × 6 13/16 × 9 7/16	T, M, M1	Marine, RV, commercial vehicles
34	260 × 173 × 200	10 1/4 × 6 13/16 × 7 7/8	A	Automotive, marine starting
35	230 × 175 × 225	9 1/16 × 6 15/16 × 8 7/8	A, A2	Automotive
65	306 × 192 × 192	12 1/16 × 7 9/16 × 7 9/16	A	Automotive
GC2 (6 V)	264 × 183 × 277	10 3/8 × 7 3/16 × 10 7/8	UT, LT	Golf cars, floor machines
4D	527 × 222 × 250	20 3/4 × 8 3/4 × 9 13/16	A, B, A2	Large RV and marine banks, commercial
8D	527 × 283 × 250	20 3/4 × 11 1/8 × 9 13/16	A, A2, B, B1	Large RV and marine banks, commercial

Source: Battery Council International group size chart, “Maximum Overall Dimensions”. BCI states that designs and designations are supplied for reference only and that dimensional details should be confirmed with the battery supplier. The “typical uses” column is general guidance, not part of the BCI chart.

What a group number tells you, and what it does not

A BCI group number describes an envelope: maximum length, width and height, plus the terminal styles and layouts listed for that group. A suffix often matters. For example, Group 27 and 27R have the same maximum dimensions in BCI’s chart but a different cell layout and polarity figure (an R suffix commonly indicates reversed terminal positions), and 31A and 31T share the same case size but list different terminal types.

The group number does not tell you:

• Capacity. The amp-hour and cold-cranking figures in BCI’s chart are reference ranges for original-equipment lead-acid batteries. They do not describe a lithium battery in the same case.
• Chemistry or voltage. A Group 31 case may hold a 12 V lead-acid, AGM or LiFePO4 battery.
• Exact terminal height and hardware, which affect lid clearance and cable routing.
• Hold-down features. Brackets that clamp a base ledge may not fit a lithium case with a different base.

Why LiFePO4 capacity in the same group size varies

LiFePO4 is lighter and more compact than lead-acid for the same energy, so suppliers fit different amounts of capacity into the same group envelope depending on the cells, the BMS and the internal layout. That is why you will see several Ah ratings sold as “Group 31”. Compare batteries on watt-hours, which for a 12.8 V nominal LiFePO4 battery is roughly the nominal voltage multiplied by the rated amp-hours:

Rated capacity (12.8 V nominal)	Nominal energy
100 Ah	1,280 Wh
200 Ah	2,560 Wh
300 Ah	3,840 Wh

Which capacity fits which case depends on the model, so ask for the drawing of the exact model you are considering rather than relying on the group label. Usable energy also depends on the BMS limits and temperature, which is another reason to read the datasheet.

Terminals and polarity

The BCI chart uses letter codes for terminal types. The ones you will see most on deep-cycle and marine batteries are:

• A: SAE automotive tapered top post.
• A2: EN/JIS tapered top post.
• T: threaded stud terminal.
• M: marine terminal, combining a tapered post with a threaded stud.
• M1: marine terminal with a hex nut.
• B: the bus-style terminal listed, along with A and A2, on large cases such as 4D and 8D.

Lithium batteries sold in group-size cases often use threaded studs or inserts instead of tapered posts. Before ordering, check three things: the terminal type matches your cable lugs (or you have adapters), the positive and negative terminals are on the same sides as your existing cables, and the terminal height plus lug and nut still clears the battery box lid.

DIN and EN size equivalents

Outside North America, batteries are often described by DIN or EN codes such as H6 or LN3. BCI publishes a reference table relating some of these to BCI groups. A few examples:

BCI group	DIN / EN reference	Max L × W × H (mm)	Max L × W × H (in)
47	H5 / LN2	242 × 175 × 190	9 9/16 × 6 15/16 × 7 1/2
48	H6 / LN3	278 × 175 × 190	11 × 6 15/16 × 7 1/2
94R	H7 / LN4	315 × 175 × 190	—
49	H8 / LN5	353 × 175 × 190	13 15/16 × 6 15/16 × 7 1/2

BCI presents this table as an estimate of which group corresponds to which DIN/EN reference size and disclaims its accuracy, so treat it as a starting point and confirm with a drawing. Note that the DIN/EN-style groups have a different width and height (175 mm wide) from Group 24, 27 and 31 (173 mm wide), so they are not interchangeable without checking the tray.

One larger case or two smaller ones?

RV and boat owners upgrading to lithium often choose between replacing two batteries with one larger case, or keeping two group-size batteries in parallel. Neither is right for every installation:

• One larger case (for example a 4D or 8D envelope) means fewer interconnecting cables, but the tray, hold-down and access must suit its length and weight.
• Two smaller cases (for example two Group 24 or 27 batteries) can reuse existing trays and are easier to lift, but need matched models and correctly sized cables, and parallel operation must be allowed by the battery model’s datasheet.

Measure both options against the space before you compare prices, and check the total energy in watt-hours rather than the group label.

How to check a LiFePO4 battery will fit

1. Measure the space, not the old battery. Record the internal length, width and height of the box or tray, and the clearance to the lid.
2. Note the terminal side and type of your existing cables, and whether the cables can reach a different terminal position.
3. Check the hold-down. Note whether it uses a top bar, a strap or a base clamp.
4. Ask for the model’s dimensional drawing, including terminal height and any handles, and compare it with your measurements.
5. Check ventilation and temperature. Lithium batteries need the charge temperature range stated on the datasheet. Cold engine rooms and hot battery boxes both matter.
6. Check the charging system. Your charger, alternator or DC-DC charger and solar controller need a LiFePO4 profile; a fit check is not only mechanical.

Private-label buyers: what to specify for a group-size case

If you are building a range for resale, the case is part of the product. When you request quotes, specify:

• The BCI group envelope, and the maximum dimensions including terminals.
• The target capacity, and the voltage (12.8 V nominal in most RV and marine ranges).
• Terminal type and polarity layout matching what your customers’ cables expect.
• Handles, hold-down features and IP rating needs for marine or outdoor use.
• Features such as Bluetooth monitoring or low-temperature charge protection, if your market expects them.
• Label and box artwork, with the model name matching the test documents.

Sourcing group-size LiFePO4 batteries through LJY

LJY Energy is a Shenzhen-based LiFePO4 battery supplier and OEM/ODM supply-chain coordinator, not a factory. For RV, marine and private-label buyers, we match your capacity target to available case sizes and provide the dimensional drawing for each model on request. Certification for your market is available and arranged per project, with certification and testing fees borne by the buyer.

Browse our 12V LiFePO4 battery series, the 12.8V RV and marine private-label program, the 12V OEM battery block, a larger-capacity example in the 12V 300Ah LiFePO4 battery, or our marine battery solutions.

FAQ

What are the dimensions of a Group 31 battery?

BCI lists maximum overall dimensions for Group 31A and 31T of 330 × 173 × 240 mm (13 × 6 13/16 × 9 7/16 in). The two share a case size but list different terminal types.

Is a Group 24 the same size as a Group 27?

No. They share the same maximum width (173 mm) and height (225 mm), but Group 27 is longer: 306 mm against 260 mm for Group 24.

How many amp-hours is a Group 31 LiFePO4 battery?

There is no fixed figure. The group number defines the case envelope, not the capacity, and different LiFePO4 models fit different capacities in it. Compare models on watt-hours and check the drawing of the exact model.

What is the difference between 4D and 8D?

Both have a BCI maximum length of 527 mm and height of 250 mm. The 8D is wider: 283 mm against 222 mm for the 4D.

Do group size numbers include the terminals?

Yes. BCI lists maximum overall dimensions, which include the terminals. Still check terminal height with the lug and nut fitted against your lid clearance.

What does the R in Group 27R mean?

An R suffix commonly indicates reversed terminal positions. In BCI’s chart, Group 27 and 27R have the same maximum dimensions but a different polarity layout, so check the terminal positions against your cables before ordering.