6 or 12 That is the question

[Cummins12V98]

Friends just bought a new 32-34' Cougar 5er (much better quality than I expected) . They have not added the batteries yet at the Dealer. They have a Solar Panel on the roof and a 2,000 Inverter. I told them to be sure they get two 6V batteries and when asked why I couldn't give an exact reason other than it's the best way to go.

So please help either tell me I am wrong and why or that I am correct and why.

Thanks!

[ReneeG]

We dry camp a lot and use our solar for TV, Satellite, and computers, plus lights and charging. We have four 6V deep cycle batteries and we only have 300 watts of solar panels!

[wopachop]

It's got 2 fridges? Both residential?

Sounds like a nice trailer. I dont think 6v is the best choice for newer trailers running solar and large inverters. I would advise him to start researching lithium. Will cost more, but it doesnt seem like they're looking for a budget friendly setup to begin with.

If they need time to decide you could always borrow a 12v battery from a car just to get by for a camping trip. Assuming they will be on shore power. Make sure they know they need a battery in the trailer for the emergency brake.

[time2roll]

Either option is inadequate for a 2000 watt inverter.

The less the dealer does the better. Smallest 12v is fine to get you home. Then you can do a proper install with 3 or 4 lithium batteries. 😉

[dedmiston]

Why stop at two batteries? If you can fit four, add four or more.

If I could only have two batteries, I'd go with two x 12v in case one went bad. With more than that though, my choice is always 6v since I could always limp by with just two 6v.

[Veebyes]

Generally pack as many amp hours as you have space to put them.

Typically RV builders don't allow much space for the battery bank. Enough room for 2 group 27 12V or 2 group 31s if you are extremely lucky.

A third option is to have a single 4D battery which will give more than 200 amp hours & simplify wiring.

It is not as simple as 6V or 12V.

There is use & battery chemistry to consider. Cheapest is not necessarily the best overall.

You can get AGM batteries. They cost much more than wet cells, have zero maintenance, are good for deeper discharges, many more discharge cycles, self discharge at half the rate of a wet cell in storage and can have a useable lifespan up to 10 years.

The way to go if you want to be prepared for more than a night or two of dry camping.

For the typical weekend warrior always on hookups the wet cell bank in one configuration or another is the way to go.

[valhalla360]

wanderingbob wrote:
I read Valhalla statement about 2 six volts turning a small motor . I am glad that I had not read it years ago when for seven years I had two 6 volt golf car batteries starting a 6-71 Detroit in a dive boat !

If your motor doesn't take a lot of amps to turn and the batteries do it...there is no harm to the batteries.

I was merely referring to a common situation where deep cycle batteries are commonly used to power starter motors.

[wanderingbob]

I read Valhalla statement about 2 six volts turning a small motor . I am glad that I had not read it years ago when for seven years I had two 6 volt golf car batteries starting a 6-71 Detroit in a dive boat !

[valhalla360]

Deep cycle batteries have a smaller number of thick plates.
Starting batteries have a larger number of thin plates.

Maximum amperage is a function of plate surface area. So more thin plates allow for more surface area and thus more amps...very useful turning over a big truck diesel.

Thicker plates allow you to take the charge down lower with less long term damage...very useful for deep cycling low to moderate house loads.

A 2000w inverter will be pulling less than 170amps
A 6-7liter diesel may be pulling 700-1000amps when starting but only for a few seconds

6v golf cart batteries are true deep cycle batteries.
The 12v trolling motor/combo batteries are relabeled starting batteries.

So for the same amp-hr rating, you won't see much difference initially but if you really use the capability, the available amp-hr in the starting batteries will drop more quickly as they wear out. If you only rarely boondock, you may never notice.

You can use deep cycle batteries for starting and it will cause them no damage. The issue is you will need more of them to develop enough amps. Quite common on cruising sail boats where you are turning over a small 20-40hp motor. It doesn't take a lot of amps, so the battery bank set up for house loads has plenty of cranking amps to turn over the small motor.

[Grit_dog]

Cummins12V98 wrote:
Interesting there are so many different opinions on this.

Grit Dog says two 6v all the way so I will side with him as y'all know we agree on everything. :B

:C

[pianotuna]

ssthrd wrote:
Which is better-- 2x6V deep cycle or 2x12V deep cycle for boondocking? My setup right now is 2x6V which gives me 260 ah. I found 2x12V that will give me (2x150=) 300ah. Are the 12's really better than the 6's?

If you have HIGH draws yes the 12 volt are better (though probably not cheaper)

If you don't have high draws, the 6 volts may have greater cycle life.

[Cummins12V98]

Interesting there are so many different opinions on this.

Grit Dog says two 6v all the way so I will side with him as y'all know we agree on everything. :B

[ktmrfs]

ssthrd wrote:
Which is better-- 2x6V deep cycle or 2x12V deep cycle for boondocking? My setup right now is 2x6V which gives me 260 ah. I found 2x12V that will give me (2x150=) 300ah. Are the 12's really better than the 6's?

assuming you keep your amp draw to 30A peak or so, I'd go with 6V. that is typical load is some LED lights, a gas fridge, an exhaust fan.

Now a pair of 6V GC2, 250AH useable AH is 250*0.75 about 180-190AH. That's correct, you can discharge typical GC2 batteries down to 25% SOC and STILL get hundreds of cycles out of them. Trojan std GC2 is 500 cycles @ 75% DOD. Compare that to a very good set of 12V that give you life at 50% DOD, even trojan 12V deep discharge cycle life drops like rock once you go below 50% DOD. So the 300AH 12V give you 150AH cycle life at 50%. Advantage goes to GC2.

[ssthrd]

Which is better-- 2x6V deep cycle or 2x12V deep cycle for boondocking? My setup right now is 2x6V which gives me 260 ah. I found 2x12V that will give me (2x150=) 300ah. Are the 12's really better than the 6's?

[wa8yxm]

Actually Group 31 are about 130 but wait there is more (27/29 are about 100)

Most of the "Group xx" batteries out there are either straight up starting or MARINE/deep cycle.. these batteries should be kept fairly full for best life. Rapid againg sets in around 75% (M/dc) or 80%(Starting) where as a TRUE Deep Cycle can go to half full before that happens.. or so they say. NOTE there will be differences berand to brand. Also the ability of the battery to recover from an "OH C**P!" level run down (like the volt meter has only one digit run down) is better with the DEEP CYCLE.

GC-2 (Golf Car, takes 2 to make 12 volts) and GC-12 (Golf Car, 12 volt) are DEEP CYCLE batteries.

LiFePo4 is even better, and more costly and other things that matter some good some not so much... (I'm just starting to play with those)