Check out Deka (East Penn Mfg) website. They are good batteries and have full specs on their batteries. GC-15 is their part number for a 6 volt "golf cart" battery that is used on a lot of electric equipment (scissor lifts and such) due to strong output down to very low voltage and strong recharge life. Putting in two sets of two batteries with a switchover would give great long use. That way you run on one set while the other is charging on your solar panel (a must for long term boondocking) and then when you get low, you can switch over to the charged pair and let the other pair charge with no load on them (the best way to charge is with no load). That's my recommendation if you plan to camp without shore or generator power. I personally use two group 27 12 volt batteries connected together because I never go without power, they are just reserve for lights, fridge and jacks when setting up, traveling, etc.