Recently bought our first travel trailer, and it has been quite the education, including understanding the dual electrical system. One thing I am thinking about doing is adding a 2d battery. I have a 12V of uncertain age (appears to be no more than 3-4 years old) and want to add a second battery for added off line power. Should I just add a second 12V or go for 2 new 6V gold cart batteries?

Two 6 volts would be my choice if you can swing it and have the room. One 12v battery won't cut it for much dry camping

DO NOT mix battery ages.2-6 volt batteries will give you approx equal power as two gp24 dual purpose batteries.

donn0128 wrote:DO NOT mix battery ages.2-6 volt batteries will give you approx equal power as two gp24 dual purpose batteries.Not quite. Two 6v deep cycle will give you approx 220-230 AH. Two Group 24 batterys (12v) will give you approx 160-170 AH.

Make sure the larger 6V will fit where you are installing them. Two rules of thought here. 6V do offer more run time, but if one goes bad then you've only got one 6V. Probably doesn't happen often enough to warrant concern. Just some food for thought.

donn0128 wrote:DO NOT mix battery ages.Keeping in mind though that one has the choice to run two 12 volt batteries paralleled together or independently, in which case battery age makes no difference at all. One can do this manually by simply connecting just one battery at a time or for greater convenience with a battery disconnect switch such as the Blue Sea m-Series 6007. That to me makes far more sense than disposing of a battery just a few years old if it's otherwise working fine and not yet anywhere near the end of it's service life.

12V vs 6V | Good Sam Community

SoundGuy
Explorer
Nov 30, 2015
TBammer wrote:
I think for now I will add a 12v in parallel. The trailer has an angle iron trough that would easily take another one.

Paralleling an aging battery that's already seen several years of service with a brand new one off the shelf is a poor idea ... far better to run each independently from the other, switching to the second battery when the first has been depleted to ~ 50% or ~ 12 volts unloaded. As already mentioned you can do this manually or for greater convenience with the use of a switch such as the Blue Sea version I referenced to earlier.
Huntindog
Explorer
Nov 30, 2015
The risk of a failed cell in a 6 volt setup is overblown.
A single 12 volt battery has 6 cells. Two 6 volts have 6 cells.. So all things being equal, a single cell going bad would be the same failure rate with either... But all thing are not equal. The 6 volts have a much more robust construction and will most always far outlive a 12 volt
12 volt fans tend to worry about cell failure as they are used to it happening on their 12 volt batteries.

6 volt fans realize the the odds of a cell going bad in a 6 volt setup is much lower... So they don't worry about it.
Huntindog
Explorer
Nov 30, 2015
SoundGuy wrote:
ktmrfs wrote:
If you dry camp a lot, then a pair of 6V has an advantage of more AH ...

Not necessarily ... a pair of G31 12 volt deep cycle batteries will offer similar AH capacity to a pair of GC-2 6 volt batteries. Apples to apples. ;)The problem is that two 31s won't fit on most TTs
standard battery mount setup. Two 6 volts will fit there nicely..

ktmrfs wrote:
... and the ability to withstand hundreds of discharges to less than 50% of capacity. Something 12V aren't real good at.

Also, if you intend to run a very heavy load (>100A) like inverters etc. for > a few minutes at at time, and do it fairly often then 12V offer an advantage in that they have lower internal resistance and are much better at high current draw situations.

I would be interested in seeing supporting documentation to both these claims as my primary interest in upgrading to dual batteries from my current single G27, aside from the fact it's now 8 yrs old, is that I am now running a 1K inverter for those times we don't have on-site shore power available. My current single G27 has handled the task surprisingly well so far but a dual set of 12s or 6s would obviously make the most of what this inverter can do for us. As such I'd be interested in any further information regarding these two claims ... got any links? :@
chr_
Explorer
Nov 30, 2015
Get two new 6V GC2's.
Keep the 12V as a spare, in the truck. If you need it you have it. You just use either-or (2X6V or 1X12V)

Wiring two 12V batts in parallel will not give you the same capacity, the plates are smaller in them. Also, if one gets a bad cell, It can damage the other battery. This does not happen with 6V batteries in series. I have a *marginal* cell in one of my GC2's. If I was running 12V, I'd have had to replace them already.
TBammer
Explorer
Nov 30, 2015
Well, you all having given a lot to consider, most of which I never even began to consider when I wrote the question. I thank everyone for their responses. I think for now I will add a 12v in parallel. The trailer has an angle iron trough that would easily take another one.
avoidcrowds
Explorer
Nov 30, 2015
Regardless of which way you go with batteries, I would recommend at least 100w of solar. 200w would be better, which is what I now have. If you go dry camping (boondock or just no hookups at a campground), your batteries can recharge every day, if the sun cooperates.

I have never needed a generator, but I also camp out west where it cools off every evening so no AC is needed. We have a 12v fan if it gets too warm inside during the day, but we usually are not inside during the day, so even the fan is not used.

I love our solar, and the peace of mind it brings.
Boon_Docker
Explorer III
Nov 30, 2015
The HM426 box is the one I have, it is a good box and 2 6v's fit nicely.
SoundGuy
Explorer
Nov 30, 2015
SoundGuy wrote:
I've got the trailer tongue space for a dual battery setup, can toss the spare G27 in the back of the truck, so it's just now a matter of deciding how I'm going to mount a dual set of batteries on the tongue. My preference is a Stanley 28" Fat Max toolbox but the G31s are too long, the GC-2s are too high. It's an issue that can easily be solved with purposed designed aluminum boxes but it's not a viable $$$ solution considering my limited use for these batteries so I may have to resort to conventional plastic battery boxes designed for the purpose ... not my preference but it'll work.

Quoting my own post here :W but regardless of whether I settle on dual 6 volt or dual 12 volt batteries my preference is to contain both batteries in a single box rather than two separate boxes. Darn, that Stanley 28" Fat Max toolbox just isn't the right size inside to accommodate either :M but I've just discovered that NOCO offers a battery box Model HM426 which is designed to hold dual 6 volts such as T-105s. According this NOCO Battery Box Info the HM426's exterior measurements are 18.25" long x 14.25" wide x 14.00" high ... length and height are no problem for me so if my tape measure shows I can accommodate the width of this box between the trailer's front wall and the two propane tanks which sit just aft of the tongue jack that's going to help tilt my decision in favour of a pair of 6 volts. :p
SoundGuy
Explorer
Nov 30, 2015
ktmrfs wrote:
If you dry camp a lot, then a pair of 6V has an advantage of more AH ...

Not necessarily ... a pair of G31 12 volt deep cycle batteries will offer similar AH capacity to a pair of GC-2 6 volt batteries. Apples to apples. ;)

ktmrfs wrote:
... and the ability to withstand hundreds of discharges to less than 50% of capacity. Something 12V aren't real good at.

Also, if you intend to run a very heavy load (>100A) like inverters etc. for > a few minutes at at time, and do it fairly often then 12V offer an advantage in that they have lower internal resistance and are much better at high current draw situations.

I would be interested in seeing supporting documentation to both these claims as my primary interest in upgrading to dual batteries from my current single G27, aside from the fact it's now 8 yrs old, is that I am now running a 1K inverter for those times we don't have on-site shore power available. My current single G27 has handled the task surprisingly well so far but a dual set of 12s or 6s would obviously make the most of what this inverter can do for us. As such I'd be interested in any further information regarding these two claims ... got any links? :@
pianotuna
Nomad III
Nov 30, 2015
Hi,

The ultimate system for the OP would be to go with a drop in LI unit. That may be cost effective from the point of cycle life. The greatest advantage is not needing to get to 100% state of charge for all cycles. The greatest disadvantage is that LI doesn't allow recharging below -20 C (-4 f).

3000 cycles to 80% depth of discharge for LI vs 1200 cycles to 50% for lead acid.

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