What happens when batteries are low in charge?

Batteries need to be the same age and from the same manufacture for best performance. Don't know where you came up with those numbers as they aren't group size numbers. Group 24 are about 85 Ah, the next size larger is group 27 at 95 to 105 Ah as typical 12 volt batteries in campers. Then there are GC-2's or golf cart batteries which are 6 volt. Properly cared for true deep cycle batteries can easily last 8 to 10 years.