The State Ports Authority's Wando River terminal is also in Mount Pleasant. Charleston is the largest city near Mount Pleasant, although Mount Pleasant is quite large in its own right. Here is a map of the Charleston area.
Group means battery physical size, ie group 24 and group 27 as mentioned earlier. Its CCA/MCA rating that counts. I have two batteries, one is 1000 cca's the other is 600 cca's (cold cranking Amps). The 1000 is the starter battery, the 600 runs accessories and is a back up starter. The higher the CCA rating, the more starting power you have. This is oversimplifying it but it gives you an idea of what a battery rating means.
These numbers are referring to the BCI Group Number of the battery. These numbers define the physical dimensions of the battery case. This is important as some applications call for specific case sizes. The BCI does not determine the Amp Hours (AH) rating for the batteries, however, but there is a correlation between case size and AH rating. For deep cycle batteries, the larger the case size the more capacity the battery will usually have.