Group 31-MDC Automotive Batteries

3D rendering of the BCI (Battery Council International) Group 31-MDC battery for cars and trucks.

Electrical Specifications:
12 Volts
-1 Cold Cranking Amps (CCA)
-1 Reserve Capacity Minutes
Left Positive Polarity

Mechanical Specifications:
Length: 13" (33.0 CM)
Width: 6 11/16" (17.1 CM)
Height: 9 1/2" (24.1 CM)
Body Style: Cutaway with Flat Classical top
Terminals: Post and Threaded
Flanges: None

Electricals:

   We measure battery power with two numbers: Voltage and Capacity.  All 31-MDC batteries provide 12 Volts and strong international standards have made sure that everyone agrees on what Voltage means and how to measure it.  Capacity, however, varies between manufacturers and brands.  To complicate matters further, we measure automotive battery capacity in a variety of ways.
   Capacity measures the number of electrons a battery can provide.  In general, we measure battery capacity in amp hours, or watt hours, however, in automotive applications, we care more about how much electrical power a battery can supply instantaneously to start the engine.  We measure this instantaneous power in CA, Cranking Amps, and CCA, Cold Cranking Amps.  Batteries store chemical energy and release it through temperature sensitive chemical reactions.  In cold climates, we only care about CCA, because they report how much instantaneous power the battery can supply at zero degrees Fahrenheit.  When new, Group 31-MDC batteries must provide a minimum of -1 CCA to meet standards but many manufacturers exceed the requirements.
   Modern vehicles increasingly rely on their batteries to power peripheral electrical features like sound and entertainment systems, navigation computers, USB ports, light bars, winches, inverters, communications devices, and countless other specialized electrical equipment.  We call these features deep cycle applications because they draw smaller amounts of power over longer time periods.  We measure deep cycle capacity in Amp Hours or Reserve Capacity Minutes.  To meet specifications, new group 31-MDC batteries must provide at least -1 Reserve Capacity Minutes but many batteries exceed these capacity requirements.

Mechanicals:

   Group 31-MDC batteries have Cutaway body shapes with overall dimensions of: 13" X 6 11/16" X 9 1/2" or 33.0 CM X 17.1 CM X 24.1 CM.  The 9 1/2" (24.1 CM) height includes the Flat Classical top and the terminals plus any protruding acid caps, but not any raised lifting straps or handles.
   Vehicles can fasten group 31-MDC batteries with top mounted hold down straps/bars, and connect electrically via leads fit for Post and Threaded terminals.

Example Battery Images:

More example images coming soon.  

Where to Buy: