Each battery is 6 volt and 225 amps. Wiring a pair "in series" gives 12 volt and wiring two "in series" pairs "parallel" give 450 amp. Try to keep your cable as short as possible with a little flex and keep them the same length between batteries. Build your own using flexible welding cable if you have the option.
"in series" means wiring positive(+) to negative (-)
"parallel" means wiring positive(+) to positive(+) and negative(-) to negative(-).
"in series" red to black
"parallel" red to red and black to black.
"in series" adds total number of volts.
"parallel" adds total number of amps.
This is the 12 volt battery that came with our travel trailer. Under each of the two removable caps are three cells (each cell is 2 volts) wired in the battery case "in series", pos(+) to neg(-). Each time you wire "in series" you add the volts. Two banks of three 2 volt cells equals 12 volts.
This is a 6 volt battery with the cap removed and you can see the three 2 volt cells.
This shows two 6 volt batteries wired "in series" to form one large 12 volt battery. Now a total of six ( 3 in each battery) 2 volt cells are wired to form 12 volts. If you couldn't see the half red-half black cable in the middle, it would look like a standard 12 volt battery. Positive on the upper left and negative on the lower right.
This photo shows how this setup (now one large 12 volt battery) would be hooked up if this was all you were using. Positive (red) cable on the upper left and negative (black) cable on the lower right side.
I have now doubled the two battery setup and the red cable on the left and the black cable on the right are wired "parallel" (pos to pos and neg to neg). Just like your dad taught you to use "booster cables", red to red and black to black. Now this forms one very large 12 volt battery bank.
To hook up this battery bank you will want to use the positive and negative posts that are the farthest apart, thus drawing current from all over the battery pack, this photos shows the positive (red) cable attached to the upper left and the negative (black) cable attached to the lower right. Please use an appropriate size fuse in the red cable. The fuse size should be about 20% larger than the amps you will be drawing out of the battery bank at any given time.