Many vehicles can accommodate more than one group size.
CCA is critical for good cranking ability. It's the number of amps a battery can support for 30 seconds at a temperature of 0 degrees F until the battery voltage drops to unusable levels. RC helps to power your vehicle's electrical system if the alternator fails. In general for both CCA and RC, the higher the number the better. The number of hours you'll be using the equipment Multiply the Amps by the Hours to determine the Amp Hours, or AH, required.