The Battery Council International (BCI) group number is a specification for the physical dimensions, terminal type, voltage, and terminal placement of a battery. All BCI 31 batteries will be close to the same size, will have the same terminals, and the same voltage. Capacity construction and chemistry are up to the manufacturer.
A 31 and a 27 are slightly different size. IIRC the footprint of a 31 is only slightly longer than the footprint of a 27, but the 31 is substantially taller. Any retailer who sells batteries will have a BCI manual, since it contains the list of what battery size goes into each car, truck, motorcycle, RV, tractor, etc. model. A31 is generally a diesel starting battery, higher in capacity than a 27 starting battery, intended for installation in over the road trucks. Think of it as a smaller alternative to a 4D or 8D. Big truck diesels need starting current in the range of 900-1100 amps. You would commonly find 2 or more in the battery box of a truck. My 36hp Westerbeake diesel needs 175 amps starting current. Total amp hour capacity means more time on the hook so capacity is more important to me than starting current, so all my batteries are deep cycle. Because of certain factors in battery construction, more cranking amps generally means less amp hour capacity, and vice versa. Since my battery compartment is not tall enough for a bank of 6 volt golf cart batteries (which have a lot more capacity than any 12 volt automotive type) or a deep cycle version of a 31 (which I think is actually a group 29, but I may not remember correctly) I use group 27 deep cycle batteries with 120 Ah capacity for the boat - 4 for the house bank and 1 for starting. The 27 deep cycles I use give about 400 cold cranking amps, which is way more than needed to start the engine. I also have a smaller group 24 deep cycle ( 84AH ) under the v berth dedicated to the anchor windlass and Lectra-San. Think about what your requirements are, and your priorities for the batteries. Measure the space you have available. Then go to Auto Zone, Walmart, or Canadian Tire to see what will fit in the BCI manual they should have posted near the battery rack. Rick Brass Sent from my iPad > On May 1, 2014, at 17:28, [email protected] via CnC-List > <[email protected]> wrote: > > Can someone with knowledge explain difference between group 27 and 31 > batteries. Will 31s fit in same box as 27s? > Thanks. Need to replace house this year. > Bill Walker > C n C 36 > > Sent from my HTC > > _______________________________________________ > This List is provided by the C&C Photo Album > http://www.cncphotoalbum.com > [email protected]
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