Parallel batteries and a question regarding reserve capacity

Forget "Reserve capacity" that only applies to starting

Two Group 31's about 130 amp hours each means you have 260 amp hours of which you can use about 25%. unless they are full DEEP CYCLE (in which case Reserve Capacity likely won't be specified) in which case you can use 50%. so you have about 75 amp hours of safely usable power before you damage the batteries.

Now with a pair of GC-2 Flooded wet cells you'd have 220 total amp hours and 110 usable (50%) since they are true DEEP CYCLE