Reserve Capacity and physical size. Reserve capacity is the amount of time a fully charged battery can deliver 25 amps at 80*F before reaching 10.5 volts. When looking for deep cycle batteries, that's the number to compare. The physical size with batteries is also a player. The bigger the battery, the more plates it has, the bigger the plates are and the more electrolyte it holds. If my customers have the room, the one I usually try to sell is the group 31. Usually the 31-5. If I remember right, their reserve capacity is 185 minutes. That's a ton. That's what you're looking for. Remember, don't compare CCA, because a deep cycle battery will have a lower CCA than standard automotive batteries by design. It's the reserve capacity that's important.
