Well here is my read on this:
1) 2 6 volt batteries are wired in series and the converter's output is hooked up by putting the (+) wire to one battery and the (-) wire to the ground post of the other battery. A short 2 gauge or larger wire connects the 2 batteries. The connecting wire should be as BIG as possible (even 0 gauge) because the connecting wire is treated the same as "internal resistance" in a 12 volt battery.
2) Gel batteries (even deep discharge ones) are maintenance free, but that is their ONLY advantage. The have a VERY high price per amp hour and the have very few amp hours compared to a standard lead acid maintenance type.
Typical gel house batteries have about 200 AH and two 6 volt gel type batteries double the volts and not the AH when in series. So you will spend a LOT of money for 200AH of capacity. Gel Golf Cart Battery
In this case 750 plus shipping for 200AH
With a flooded lead acid maintenance battery system you can get 2 6 volt Trojan batteries (top of the line) http://www.batteriesinaflash.com/dee...-cycle-battery
putting out 235 AH at 12 volts for about 400 plus shipping.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW