Car Battery Size Chart: BCI Group Dimensions

A battery group size is a case specification, not a performance one. It fixes the length, width and height of the box and where the terminals sit — nothing else. Two batteries in the same group can differ enormously in capacity and still both fit. The tables below list every passenger-car and light-commercial group as the Battery Council International publishes them, with the heavy-duty commercial groups after.

What a group number actually fixes

The group number answers one question: will it go in the tray, will the hold-down clamp it, and will the cables reach the right posts. It says nothing about how much current the battery delivers or how long it lasts. That is why a group 34 can be sold anywhere from about 235 to 1,000 cold-cranking amps — same box, very different battery.

Terminal position is the part that catches people out. A group number with an R suffix is the same case with the polarity reversed, so a 34 and a 34R are dimensionally identical and electrically mirrored. Fitting the wrong one leaves the positive cable stretching diagonally across the top of the battery, which is exactly the arrangement that eventually shorts against the bonnet.

Finding your group size

In order of reliability: the label on the battery already in the car, then the owner handbook, then a parts lookup by registration or VIN. Measuring the tray works as a cross-check but not as the answer on its own, because two groups can share a footprint and differ in height, and height is what fouls the bonnet.

BCI passenger car and light commercial groups, 12 volt

Dimensions are maximum overall case size. Cold-cranking figures are the range of original-equipment ratings published for that group, given at 0 °F, and are there to show the spread rather than to specify any particular battery.

Heavy-duty commercial groups, 12 volt

BCI to DIN and EN sizes

European-fit batteries are often labelled with a DIN or EN code rather than a BCI group — H6 and H8 are the two seen most. The mapping below is published by BCI itself, which describes it as a best-fit estimate rather than an equivalence, so treat it as a starting point and check the case dimensions before buying.

Method and precision

Dimensions and cold-cranking ranges are reproduced from the published data book, both unit columns as printed. The two columns are not conversions of one another — they are maximum case dimensions rounded independently, so 175 mm appears as 6 15/16 in while 208 mm appears as 8 3/16 in. Carrying both as published is what allows a mistyped digit to be caught, since a slip moves one column and not the other. No vehicle-fitment column is given: fitment changes model year by model year and no primary source publishes it, so the honest answer is the label on the battery in the car. Sources: Battery Council International Battery Replacement Data Book — "BCI Group Numbers, Dimensional Specifications and Ratings" and the "BCI / DIN / EN Reference Chart".

Changing a battery without incident

Negative terminal off first and back on last. With the negative disconnected, a spanner that slips off the positive post and touches bodywork does nothing; with it connected, the same slip welds the spanner. Insulated tools are worth having for the same reason.

Terminal clamps corrode into an oval and then will not release. Spreading the clamp rather than levering it off the post protects the post, which is soft lead and deforms permanently. A puller is the tool for a clamp that has bonded.

Most modern vehicles lose stored settings when power is removed, and some need a relearn afterwards for idle, windows or the charging system. Check before disconnecting rather than after.

Battery work tools are in automotive tools, spanners and insulated tools.