Two 6 volt batteries or two 12 volt batteries ??

Well the OP has lots of good advise but it all comes back to what his goals are and his usage.

We do not boondock in the true sense but we will spend a day or two without electric if we need to. I have a four day event every years so I just tote my trolling motor battery to carry me over the last day or so.

I works fine for the once or twice a year I need extra battery power. If I needed it more often I would go with two 12 volt batteries and a transfer switch.

RasMouSein wrote:
I have industrial "true" deep cycle 12v... 2 for a total of 430amp/h...
The local battery shop had a deal a the time, so it made sense for me.
People go for the 6v because (story goes) of the footprint, they tend to be taller and fit in the same rack. Therefore more amp/hour in the same place.

I agree... but it may not be for everyone due to cost... but you cant get something for nothing!

I also went with the true deep cycle 12v batts (US185HC) for a total of 440ah.... and the footprint is the reason.
I have room for 3 batteries and 3 6v batts just dont work in a 12v system... I only have 2 batteries at this time, but I have room for another 220ah if I decide I want it... (total of 660ah)

with 2 LARGE 6v batts, (L16HC) my limit would have been around 370ah...and not allowed for any option for continued use if 1 of them failed while out and away, whereas with 2 12v batts, the bad one can be removed from the system, and you can still carry on with the good battery... IF I had room for 4 batteries, I probably would have installed 4 6volt L16 batteries.

BUT, when one is looking at regular RV sized batteries, 2 6v batts have the ability to give much better performance over a longer period of time, than does the "regular sized" 12v multipurpose battery that is somtimes called "deep cycle" by those who dont know any better...

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.

Fishhunter wrote:
This discussion brought up a question I've been wondering about..if your TV is plugged into the TT you can run off the TV batteries...will this also charge the TV batteries when the TT is plugged into AC or running off generator?

Depends if the truck has an isolation relay to stop the backfeed. Ford does have a relay.

I use a Trik-L-Start combiner over the relay to allow my trailer solar to keep my Ford truck battery charged in storage.

Fishhunter wrote:
This discussion brought up a question I've been wondering about..if your TV is plugged into the TT you can run off the TV batteries...will this also charge the TV batteries when the TT is plugged into AC or running off generator?

Yes. as long as there is no disconnect feature on the truck. My 7 pin is live all the time.

That is where my third battery comes from.. My truck has a camper/accesorie package and uses a battery just for the 7 pin. I have a seperate starting battery.

So when boon docking my truck is always plugged in. My solar and or gen will charge the truck battery too along with RV batts.

I can get a bit over 15 amps through the 7 pin if I needed to charge the RV batts from the truck. On the chevys of my year too the ECM controls the volts and I get 14.5 volts at the 7 pin.

Just a note there is an isolator that seperates starting and aux battery..

This discussion brought up a question I've been wondering about..if your TV is plugged into the TT you can run off the TV batteries...will this also charge the TV batteries when the TT is plugged into AC or running off generator?

RasMouSein wrote:
People go for the 6v because (story goes) of the footprint, they tend to be taller and fit in the same rack. Therefore more amp/hour in the same place.

Closer to the truth ... many go for two 6 volt GC-2s because pundits here on the forum tell them that's the "better" way to go. :S In reality there's much more to the story and a pair of properly selected G31 12 volts in parallel, some of which are in fact true deep cycle despite what the "experts" here will tell you, could serve some just as well or better. Aside from the obvious advantage that if one 12 volt fails you can still "fly", another is that 12 volt jugs usually have less internal resistance, which in turn means if you're using those batts to power an inverter chances are voltage drop under heavy load is going to be less. So too do more expensive AGM batts have less internal resistance. OTOH, a pair of GC-2s will have a smaller footprint and therefore may be easier to mount than a pair of G31s. They generally also offer the biggest bang for the buck, especially flooded, as so many are sold for so many different uses, not just in RVs. So which is "better"? - you be the judge, for your own reasons, not for someone else's. ;)

FWIW, this spring I'm replacing my pooched 10 yr old flooded G27 that's been sitting on the tongue with a single G31 AGM that will be mounted in the front pass through storage compartment where the run to my 1000 watt PSW inverter will be much shorter. I'm installing only one because we most often camp with shore power available, only occasionally without it, but if we dry camped more often I'd run 2 in parallel ... personal choice. :B Keep in mind though that what batteries, how many you install, their AH rating, and charging requirements must be properly matched to the charger you intend to use to maintain those batteries ... don't get that right and you'll be replacing those batteries sooner rather than later regardless of whether they're 6 volt or 12 volt jugs. ;)

$114 bucks with 10% coupon thats - $23 bucks.

Comes to about $207 with core and without taxes..



https://www.batteriesplus.com/productdetails/sligc115

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

Yes. In that instance your options are.

1. Go out and buy another battery. You can find 6 volts without much trouble locally.
2. Disconnect the batteries and run the RV off the tow vehicles battery temporarily to get you through the weekend.
3. disconnect batts and Run off generator to get you through.

AH's are AH's... I have 3 12 volt 75 AH batts.. The thing is the space constraints..Not really weight

Ill be going to 6 volt soon. This will allow me to eliminate the 3rd battery.

The GC2 6 volts are 64 lbs. x 2 = 128 lbs.
DC 24 series are 42 lbs x 3 = 126 lbs

GC2 are 230 ah's
DC24 are 75 ah x 3 = 225 ah..

Now if you try to get a large 12 volt to match the ah of the 6's your talking space issues.

Group 31's @ 105 ah are big x2 = 210 ah's.. But still 60 lbs x2 = 120 lbs.


So do the math all you want. 2x 6 volt will win everytime IMO.

The other thing is you need a way to charge them properly of they will die a slow death..