I am still wayne_tw wrote:
When using two 6 volt batteries wired in series, you double the volts but the amp hours remain the same.
When using two 12 volts wired in parallel, you double the amp hours but the volts remain the same.
Therefore, using two 12 volt batteries you will have greater capacity for the size of the battery bank than using two 6 volt batteries.
While the first two sentences are true, the third is not necessarily true. A 12-volt battery closest in size to a 6-volt GC2 has about 100 Ah. Two will give you 200 Ah. Two GC2s will give you 220 to 235 Ah at 20 hr rate.