Its like How do you get 4 Elephants into a Volkswagen beetle? — 2 in the front and two in the back...
The good side is the heaver the battery the more AHs it produces... Two of those 6VC Golf Cart Batteries wired in series to produce 12VC will give you between 200 an 220 AH's of capacity. That relates to your batteries producing 12VC @ 25 AMPS for around 7 hours time. I would not however ever run them below their 50% charge state so in my case I would get around 3-4 hours of drawing 25AMPS of DC Current. 25AMPS is alot of juice by the way...
Roy Ken