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BCI Battery Group Size Chart

What a BCI battery group number tells you, common group numbers by application, and what the F and R suffixes mean.

Ref FA-0075BCI

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

The Battery Council International (BCI) assigns group numbers to lead-acid batteries. A group number fixes the case's maximum length, width and height, and the terminal type and position. It does not set the electrical rating. Two group 31 batteries can have very different cold cranking amps (CCA) and reserve capacity. Exact case dimensions for each group are in the BCI Technical Manual.

How to identify

The group number is on the label, often near the CCA rating. If the label is gone, measure the case and note the terminal type (top post, side post or threaded stud) and which side the positive terminal is on, viewed from the front.

Common group numbers

Group	Terminal style	Typical applications
24 and 24F	Top post	Cars, light trucks, marine and RV
27 and 27F	Top post	Light trucks, marine and RV deep cycle
31	Threaded stud or top post	Heavy trucks, buses, equipment, marine
34	Top post	Cars and light trucks
35	Top post	Cars and light trucks, many Asian-make vehicles
47 (H5)	Top post	Cars and small SUVs
48 (H6)	Top post	Cars, SUVs, light trucks
49 (H8)	Top post	Larger cars, SUVs, light trucks
65	Top post	Full-size trucks and vans
78	Side post	Many GM cars and trucks
4D	Top post	Heavy equipment, large commercial vehicles
8D	Top post	Heavy equipment, large commercial vehicles
U1	Top post or stud	Lawn and garden, small equipment

Key points

F (in some groups) or R after the number means reversed terminal position compared with the base group.
Heavy trucks often run several group 31 batteries in parallel. Replace them as a matched set of the same type and age.
Pick the group that fits the tray, hold-down and cables, then pick the CCA and reserve capacity the vehicle maker requires.
AGM and flooded batteries can share a group size but need the right charger and, on some vehicles, battery registration.

Common mistakes

Choosing by group number alone and getting too low a CCA.
Installing a reversed-terminal version, so cables do not reach or are stretched.
Mixing old and new batteries in a parallel bank.

Governing standards: BCI Technical Manual (group size specifications). Vehicle manufacturer's battery requirements. SAE J537 for CCA test method.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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