Two 6 volt batteries or two 12 volt batteries ??

FrankShore wrote:
One 6v goes out and you're in trouble.

One CELL of a "12V" shorts and you are in trouble..

One shorted cell of one 12V battery when in parallel will discharge the "good" battery and will also prevent the "good" battery from recharging properly.

One 12V battery gets "weak" and the OTHER 12V battery takes a beating until BOTH no longer work.

The problem with your "theory" is the mere fact that MOST CONSUMER "12V" batteries are actually COMBINATION "starting/deep cycle" batteries which are marketed as "RV/Marine" batteries.

RV/Marine batteries are a COMPROMISE, they are designed to take the demands of high current for a short time (starting) and the demands of deep discharge (trolling motors) for a longer time than just a starting battery.

As a compromise they HAVE some drawbacks.. They do NEITHER "job" well.

They don't function as well under "starting" or a deep cycle.

IE, they don't last as long as a standard car battery in starting mode or can be deeply discharged as a real deep cycle.

A group 27 RV/marine battery has about 70 Ahr of capacity, of that you only want to use no more than 20% (14 Ahr) of that capacity for longest battery life but can be discharged to 50% (35 Ahr) at a REDUCED LIFE.

Granted, you can find true 12V deep cycle batteries (group 31), the draw back to those is not every battery shop carries them (special order) and since they are not in super high demand they ARE considerably MORE EXPENSIVE.

Hence the reason as to why 6V Golf Cart batteries are a great alternative..

6V GC batteries ARE a true deep cycle, ready available and extremely low cost per Ahr.

Typically 6V GC batts give you about 210 Ahr of capacity per pair and you will need two of these wire in series (pos of on to the neg of the other).

6V GC batteries ARE designed to be able to withstand up to 80% (168 Ahr) discharges but for max life should be limited to %50 (105 Ahr).

It would take THREE group 27 RV/marine discharged to 50% to equal one pair of 6V GC batteries at the same 50% discharge.. However the life of the group 27 12V RV/marine batteries WILL be considerably LESS and you end up spending MORE on the THREE RV/Marine batteries over the life of your RV.

If you don't boondock, then no reason to buy GC batts, but if you do boondock, you WILL get much more capacity and it WILL cost you less in the long run.

I don't boondock but I did convert my TT to a residential fridge so one pair of 6V GC batteries can easily run my fridge, some lights and even the furnace for 24 hrs before needing to recharge. It would take at least three if not four group 27 RV/marine batteries to do the same job and the service life will be much shorter..

I just replaced my first set of GC batteries this spring, the first set gave me 9 years of service and they were still working OK but I did notice that they had lost some capacity so I replaced them.. Not bad service and the replacements cost $80 each at Sam's.