Two 6 volt vs. 12 volt deep cycle

[Kevin242]

What would be the advantages and disadvantages of using two 6 volt batteries to power an RV instead of the usual single 12 volt "deep cycle"?

I see the weight of the extra 6 volt as being one disadvantage...

[Rick B]

Disadvantages are cost, weight, storage space, and perhaps the need to replace both when one fails.

Advantages are amperage (I think 220 amp hrs, much greater than one 12 volt). I have used two 6 volts with my 80 watt solar system, as I do a lot of dry camping. The reserve power is great.

Rick B

[Bigfoot Mike]

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<div class='quotemain'>Disadvantages are cost, weight, storage space, and perhaps the need to replace both when one fails.
Advantages are amperage (I think 220 amp hrs, much greater than one 12 volt). I have used two 6 volts with my 80 watt solar system, as I do a lot of dry camping. The reserve power is great.
Rick B[/quote]
What Rick B Said.

[Brian B-P]

Most of the characteristics mentioned in discussions of dual batteries have nothing to do with voltage and everything to do with capacity. The weight and bulk are the result of having so much battery that you need to buy it in two pieces (so you can lift each one!), and would apply nearly equally to two 6V batteries in series or 2 12V batteries in parallel.

In batteries, bigger is better (for reliability and efficiency), but at some point the benefit does not justify the weight or cost, or the complexity of having two. The optimal amount depends on your energy needs.

If going the two-battery route, two 6V in series is the most common; but two 12V in parallel is also done. If comparing series and parallel configurations, be careful to compare similar batteries, not comparing a pair of cheap RV/marine 12V units to a pair of industrial-grade 6V deep cycle, as is commonly done.

[Timmy G]

I wrestled with this one a few years back and went with two six volt batteries which I put in a plastic toolbox from Home Depot , then had a new back bumper put on my trailer to mount and lock them. I wanted the power so that I didn't have to worry about charging them over a 5 or 6 day adventure (yeah, I generally don't use much power in any given day). Initial cost is high (about $300 for the batteries, 30 for the tool box and $100 for the new bumper). Unlike most Deep cycle 12 V batteries, these batteries can be serviced when they start to die (probably in a few years), but that is relatively inexpensive compared to buying a new battery, so in the long term, cost is probably close.

[Frederick L. Simson]

What would be the advantages and disadvantages of using [b]two 6 volt batteries to power an RV instead of the usual [b]single 12 volt "deep cycle"?

If going the two-battery route, two 6V in series is the most common; but two 12V in parallel is also done.

I think the advantage of 2 six volt batteries is having the maximum capacity in the minimum footprint, a consideration if you are trying to utilize limited tongue space.

1. Most Common Size 6 Volt Batteries 10-1/4" long x 7-1/8" wide x 10-7/8" high @ 62 LBS.

2. Most Common Size 12 Volt Batteries 12-3/4" long x 6-3/4" wide x 9-3/4" high @ 55 LBS.

The disadvantage is the weight.

[Pete Dumbleton]

The original question is a little bit off kilter in that one normally replaces a single 12V battery with two 6V golf cart batteries RATHER than add a second 12V battery. There are several reasons, but the most important is that the system is now charging two batteries in series rather than in parallel.

Two dissimilar 12V batteries in parallel will start to have lots of problems in both charging and discharging, with the worse of the two pulling down the other one. Even if the two 12V appear similar in make and model and type, they will have different ages.

In addition to that, the 6V golf cart batteries are bigger (taller) than the 12V deep cycle batteries, so they contain more energy **for the same footprint**. Also, the golf cart batteries are designed for more charge/discharge cycles than 12V deep cycles typically are.

Battery boxes are out there for the taller golf cart batteries.

[peterh]

I'll add this thought in: When I was having troubles with a dead alternator in my tow vehicle and drained the TV battery dry it was sure nice to have this nice, fresh 12V battery that I could pull out of the trailer and move up to the tow vehicle. It started the truck and got us home . . .

--Peter

[Pete Dumbleton]

I had a similar situation where my TV battery had just about bit the dust and when I went to start it with everything connected, the egg battery's fuse blew... I just moved the egg battery within jumper cable range of the TV battery, started up, drove to the Battery Getting Place and got a new TV battery.

BTW, don't forget that many auto parts chains will check your TV battery and charging system for correct operation and some will also test the egg battery. Be SURE to wear eye protection if you are witnessing the testing because things can happen! (Had a close call myself...).

[Kevin242]

Thanks everyone for the tips...

I'm leaning toward the 12 volt for a few reasons:

1. We use very little power most of the time in our small RV, and usually camp for 2-3 days at a time.
2. I'm going to supplement the battery with a solar panel as well.
3. I'd prefer not to add the weight of two batteries.

I think though if I had a bigger RV, with more accessories, and camped frequently for longer periods, I would go with two 6 Volt batteries.

[Larry C Hanson]

Hi Kevin,

I, too, considered the two 6V option but the added tongue
weight (2 batteries and case, etc = about 125 lbs.) seemed
excessive. Ended up with one Trojan deep cycle 12v battery
(SCS-225 12V 130 Amp-hours @ 20hr rate 66 lbs.) that has
worked out very well. Think it cost about $160 8 years ago
but it still is going strong.

Larry H

[Franswa]

although the advantages of two six volt batteries are very well documented.....size does matter....as in size of trailer

If I was Kevin and Larry I'd opt for one 12 volt....battery weight as a percentage of total trailer weight becomes a consideration...finding a place to put them is another consideration...the cost/benefit analysis gets pretty sketchy...

I got my trailer with the dual battery bank...so I never had to make the decision....getting the bank to work right required some work however(DPO just dropped them in there...bad install/placement and connections and a dead converter/charger to boot !!!)

Charging the TVs battery in an emergency/breakdown would be simple if that ever happened...I do not have a converter anymore...just a very good charger and I did not mount it permanently for just such an occurence...just unplug charger at both ends and take to wherever (it comes with a set of spring clamps that plug into the output side)

if no other power supply is available.. to charge from trailer battery bank...plug inverter in (it's portable and can go anywhere too... I have two outside 12V outlets as well) plug charger into inverter and charge away....ready for anything..or just about

[Timber Wolf]

Not much to add, it has been pretty well covered above. I will say, there is no free lunch. Capacity comes from bigger and more lead, whether it be in 6V or 12V batteries. I went with two 6V because I removed a second propane bottle and heavy dual bottle steel rack from the tongue so I about broke even on weight up there. Also, two 6V batteries seemed to be the easiest and most economical way to get the most capacity. It has worked well for a couple of years and I am satisfied with my setup and decision.

[Joe Romas]

I'm surprised few people know what happens when you put 2 batteries in parallel.
See post #10 here for a good explanation.
http://www.fiberglassrv.com/forums/f...tml#post639467

Hint, the weaker draws down the stronger. Two 6 volts ones in series is a better solution.

[Joe Romas]

Originally Posted by Civilguy

Kevin posted in 2007 and was last active on this forum in early 2010.

Yeah but the subject is still of interest to some

[redbarron55]

Two 12 volt batteries must be more or less perfectly matched or one will carry the load and the other not as much.
Same with charging.
Two six volt will always share current since it must go though both equally charging and discharging.