what does group size mean on batteries
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.