2 -(6v) batteries vs 2 (12v) batteries

[tbrady]

Hi All,

I asked my dealer about getting a trailer with 2 6 volt batteries instead of a single 12 volt battery.  They spoke to Livin Lite and apparently Livin Lite recommended going with 2 12v batteries instead, something about how hot the wires can get with 6v batteries as one battery drains down.

Does anyone know anything about this or have any recommendations?  From everything I have read online it seems going with 2 6v batteries is better...

Thoughts??
thanks
tim

[DavidM]

That is pure BS from Livin LIte. What is the difference between one 12V battery where all cells are internally connected and two 6V batteries where one set of cells is connected to the other set with a wire.

Now certainly you have to use a big enough cable to connect the two  batteries, but #6 is good enough, but many use bigger. You can buy short 1' long interconnecting cables at any marine store.

And if you have the room and the capacity for the weight, two 6V batteries give you true deep cycle capability. Most 12V batteries are not true deep cycle and make compromises in their construction to be so called dual purpose.

And because they are used everywhere there is a golf course, 6V batteries are relatively cheap and give you the most bang for the buck.

The only reason to use a single 12V battery is tongue weight. A single Group 27 12V battery weighs about 60 lbs and a pair of 6V batteries weighs 140 lbs.

David

[charliem]

To second DavidM: (..pure BS from LivinLite)². Either they misunderstood or MaryJane has come to IN. Technically two 6V batteries in series are better than two 12s because all cells are in series. Batteries like series vs parallel. Go golfers.

[pjcd]

What are the cost differences?

[Merlin]

What are the cost differences?

If you compare "apples to apple" there isn't a cost savings between two 6 volt batteries in series and two 12 volt batteries in parallel. However, because flooded cell 6 volt GC2 golf cart batteries are so common and readily available, you can get them relatively very inexpensively. So they win hands down in the cost contest.

For example if you stick with real deep cycle batteries in a good brand like Crown or Lifeline, buying two 6 volt batteries will set you back as much as two 12 volt batteries, assuming the same total amp-hour capacity for each pair. As David noted above, the problem is finding real, honest, deep cycle 12 volt batteries for the comparison. And, those are spendy.

A PAIR of 6 volt GC2 batteries from a warehouse store like a Sams Club will set you back only $170. A bargain for the power available.

I think a real bargain in RV batteries is the Duracell 6VDC AGM GC2 golf cart battery available at Sam's Club for $180 each. I like AGM in an RV setting because there is no venting of corrosive gases and no maintenance. Not incidentally, two of the same brand/type of battery in 12VDC cost the same at Sams Club, so price is a wash. However, in this case the 6VDC are deep cycle and the 12VDC is dual purpose, so not true deep cycle. The 12VDC will work fine, but may not last as long deeply cycled.

[pjcd]

As they say.......................

[gbpack]

Our two golf cart 6-volt car batteries from Costco were $105 each (including tax). As mentioned, golf cart batteries are deep cycle and work great wired together in series. Last summer we camped for 4 nights with no hook-ups and our batteries were still at 50% state of charge. I highly recommend doing it that way!

[DavidM]

Let me use this thread to comment on AGM (absorbed glass matt) batteries discussed above vs more conventional flooded cell batteries. AGMs are a newish type of self contained, non venting battery capable of being mounted upside down if necessary. They are made in all sizes. Flooded cell batteries are the kind that have been around for centuries and deep cycle batteries have fill caps for adding water when necessary.

AGM Pros:

Don't require checking and adding water. This is almost a non issue for me as I check a couple of times each summer and usually add water once each year to my flooded cell batteries.

Don't offgas. Well I am not sure that this is true, but in any case it is irrelevant for batteries mounted in the open air on your trailer's tongue.

AGMs have both deep cycle and starting battery properties and there is very little difference between AGMs sold for each type of use.

Some believe that AGMs can be discharged more deeply than flooded cells without harm. I haven't seen any data to support this, but it is a pervasive view on the various boater forums.

AGMs can supply huge amounts of current when necessary and can be recharged at a higher rate than flooded cell batteries. The supply advantage is irrelevant for RV use as the typical current draw is very low. The recharge advantage has some value, particularly if you only use one battery. A single Group 27 battery has 60-70 amp hours of capacity and the normal 40 amp converter can recharge a flooded cell too fast. But a pair of 6v flooded cell golf cart batteries has enough capacity to deal with the 40 amp converter.

Cons:

Cost. AGMs cost 2-3 times more than flooded cell batteries.

So if you are willing to pay more, you can forget about checking and adding water. Otherwise there is little advantage to AGMs over a pair of 6V golf cart batteries.

David

[charliem]

So if you are willing to pay more, you can forget about checking and adding water. Otherwise there is little advantage to AGMs over a pair of 6V golf cart batteries.

David

I totally agree with DavidM's comments. I've never really understood the attraction of AGMs for the average camper. If the batteries are conventionally mounted on the tongue and you're willing to check the water level occasionally there's absolutely no advantage to AGMs except a much lighter wallet after leaving the store. Camp on!

[GoElectric]

The only way it will reduce the heat in the wires with two 12 volt batteries, is connecting them in series for 24V with half of the current as is done in a bass boat, which obviously won't work on the 12 volt system.  We are using two 6 volt golf cart batteries because we like to camp at National Forest Campgrounds, which many restrict generator use, and the 6 volt's work great.  Also, for the benefit of the extra tongue weight when tanks are low or empty, because we have the rear deck option and when loaded really lightens the tongue weight too much.

[tbrady]

Thanks for all the great information everyone!

[tinkeringtechie]

Another advantage of AGM's that could be useful for certain campers is their low self-discharge rate. A typical FLA battery has a self discharge rate of 5-10% per month, but an AGM battery is 1-3% per month. That could be helpful for solar charging or some storage situations.

[catmanriff]

I'm gettin' my learnin' on with these posts!

Thanks

[charliem]

 It's been addressed before but it's worth repeating here: If you plan on boondocking and you have a 6 cu ft two door fridge you must disable the frame heater. The two door Dometic refrigerator has an electric frame heater the sucks 0.5 Amps from the battery 24/7. This results in an automatic 12 AH draw every day that cannot be turned off.

To put this in perspective the average daily use while boondocking has been estimated at 15-30 AH/day depending on furnace use. If you add the constant frame heater draw you bump that up to 27-42 AH/day. That significantly reduces the number of days you can stay out with no real benefit. Using 15AH/day and 110AH allowable (50% of 220AH available with two GC2 golfers) your boondocking would be reduced from 7 days to 4 days. Search the archives of this forum for "frame heater" (without quotes) for details of the simple mod. 

[pjcd]

How do you disable the frame heater? Is there a fuse or switch?