6v vs 12v

[Babe2201]

if they are wired in parallel and one fails open circuit, then yes, you will still have power.
if one fails short and they are fused, the shorting current should blow the fuse and you still have power.
if the shorting current is insufficient to blow the fuse, then you will lose power rapidly.
if one fails short and you are not fused, you will have no power and a bad hair day with lots
of smoke/fire/acid/screaming.. LOL ( an exaggeration but a rare possibility )..

6V is usually deemed "best back for the buck" capacity vs cost vs lifespan is the prime mover here.

I am not going to argue that 2 6V batteries seem to be the best value in performance vs. money spent I am just pointing out a con to using them. I have not ruled out replacing my 2 12V batteries with 6V when the time comes.

 

[solarman]

The 50% Rule has little credibility as a rule of thumb because it offers very little in terms of a practical difference over ignoring it entirely. But whatever, "it can't hurt". But somehow this rule of thumb has mutated from optimizing battery life to a dire consequence of don't ever cross that line or you'll 'kill your batteries'. That's where I throw the flag and call bullcrap, it's just not true. Gary's right, few people are going to study and become battery application engineers just to go camping and use a battery, and would just like a little simple advice to follow. Telling folks they're going to kill their batteries using them as specified by the manufacturer is wrong. The discussion should center around other more important facets of battery use like charging, storage and maintenance which are by far the more predominant factors in battery life.

Mark B.
Albuquerque, NM

you do know Mark that taking your battery below 50 to say 49% will open a black hole and the end of the world as we know it.. !

 

[solarman]

I am not going to argue that 2 6V batteries seem to be the best value in performance vs. money spent I am just pointing out a con to using them. I have not ruled out replacing my 2 12V batteries with 6V when the time comes.

no argument there..

now, how about four 6V batteries, 2 series and 2 parallel ?

 

[Babe2201]

no argument there..

now, how about four 6V batteries, 2 series and 2 parallel ?

I have a travel trailer so not sure if I could find a box to fit behind the propane tanks. I would actually like to put 2 group 37 batteries in there but not sure if I can find a box that would fit and not cost an arm and a leg.

 

[Mark_K5LXP]

Generally speaking, well cared for batteries don't typically fail catastrophically. For less well cared for banks, when one fails it's bank-mates are likely not far behind condition wise so the idea of having a reserve is somewhat mitigated. The takeaway is to ensure their care and feeding, then dealing with contingencies becomes less of a consideration.

Mark B.
Albuquerque, NM

 

[vitalxs]

I am not going to argue that 2 6V batteries seem to be the best value in performance vs. money spent I am just pointing out a con to using them. I have not ruled out replacing my 2 12V batteries with 6V when the time comes.

I am new to the RVing too, and just bought an RV from my friend who was original owner. He is a retired highly decorated auto-mechanical engineer. In any case, he just told me today that he had REPLACED original 4x6V battery system which he PURCHASED as an option(!), with 2x12V system, which is what it has now, and advised me to check those batteries, as he knows they had recently were left to die due to fires.
So now, I am reading here, that 6V is considered better than 12V.
He said that he did it after original 6V batteries finally gave up, and he found himself in a situation were 6V batteries were not available or be prohibitively expensive, so he downgraded to 2x12s as, he said, they are offering similar performance, but give much more flexibility, easier to source, and cheaper than 6Vs...

 

[Mark_K5LXP]

It's tough to gauge "similar" performance because it would take a laboratory setting to ensure identical operating environment. "Close" is plausible, but generally 6V and 12V batteries are different enough based on specification and actual performance that they won't be interchangeable. There's physics with the plate construction and electrolyte distribution that they won't perform identically even for the same rated Ah. Over time and cycles they'll diverge more and the 6V modules will tend to win out. If the application is such that nothing is being particularly stressed then an argument could be made 6V would be overkill and 12V is "enough". Nothing wrong with that if it works out.

Mark B.
Albuquerque, NM

 

[Bobtop46]

I have a travel trailer so not sure if I could find a box to fit behind the propane tanks. I would actually like to put 2 group 37 batteries in there but not sure if I can find a box that would fit and not cost an arm and a leg.

I use this when I replaced my battery setup.

https://www.amazon.com/NOCO-HM426-Commercial-Automotive-Batteries/dp/B003VAUG5A/ref=psdc_15720021_t2_B002WCUR0M

 

[IBTripping]

I am new to the RVing too, and just bought an RV from my friend who was original owner. He is a retired highly decorated auto-mechanical engineer. In any case, he just told me today that he had REPLACED original 4x6V battery system which he PURCHASED as an option(!), with 2x12V system, which is what it has now, and advised me to check those batteries, as he knows they had recently were left to die due to fires.
So now, I am reading here, that 6V is considered better than 12V.
He said that he did it after original 6V batteries finally gave up, and he found himself in a situation were 6V batteries were not available or be prohibitively expensive, so he downgraded to 2x12s as, he said, they are offering similar performance, but give much more flexibility, easier to source, and cheaper than 6Vs...

First let me welcome you to the Forum. There is nothing wrong with using 12 volt batteries. Since you have them and they are fairly new, I see no need to replace them. Even though they have been depleted once, if they can still be charged, I'd use them rather than spend money on new batteries whether 6 or 12 volt.

 

[DonTom]

One disadvantage I see in a 2 battery system is that if down the road one fails you have no power.

No different than a cell shorting out in a 12V battery.

There are the same number of cells either way (six 2.2 v cells) and any of them can crap out at any time and drop your output voltage by two volts (they normally short out).

All that is different is the one wire between the two six volt batteries. There is NO advantage of a single 12V battery. The advantage of two six volt batteries in series you will find out when you need to replace them. Around half the weight for the same capacity.

BTW, the "50% rule" is avoided by going with lith batteries.

-Don- Reno, NV

 

[John From Detroit]

Correct me if I am wrong but with 2 12V batteries if one fails the other one will give you power

Depends on the faiulure mode. OPEN yes. Shorted NO and I've had 'em go both ways

But 4 GC-2 wired series/parallel. (To be honest there are no six volt batteries in RV's. just 12 volt that for ease of handling come in two pieces) are the same as 2 12 volt in parallel only 440 AMP horus of DEEP CYCLE battery.. That's a whole, whole, whole lot more than say 2 Group 29 MARINE/deep cycle in parallel. (Roughly 8 times the usable power)

 

[DonTom]

I usually see two 6V in series, so I assumed that was what was compared to a single 12V.

It is more important for batteries in parallel to be the same brand, same age, same everything. Less picky with two 6 v batteries in series and that is what I normally see, even in new RVs like the one I just purchased as well as all the others where I checked the battery compartment.

What I don't know is what those new 6V batteries are otherwise. Not a single spec mentioned on them and they are sealed. The only reason I know they are 6V is because they are wired in series. I even wonder if they could be lith since they are small.

-Don- Reno, NV

 

[Ex-Calif]

Battery arguments abound on the internet. Empirically in a deep cycling situation, there aren't many golf carts powered by 12V batteries so let's assume golf cart makers and a bazillion golf courses know what works. Two purpose built deep cycle 6V batteries are the go to for this application.

If you are going to boondock frequently and intend to deep cycle the house bank 6V is probably the way to go. This is what we did almost exclusively on the boats with up to 8 Trojans and lots of solar.

However... Most RV folks, including me, spend 90% of the time plugged in and don't deep cycle the batteries much. I haven't seen my buss voltage drop below 12.4v in the last 8 months living full tine in the RV with only two X two week road trips this year.

I run "marine" 12V batteries which are a compromise. They arguably deep cycle better than a regular car 12V. The other advantage of 2 X 12v is that if one cell fails you can take the offending battery out of the system and finish your trip. Not so if one cell in a 2 battery 6v system fails. 12V batteries amp per amp are also cheaper for a few reasons primarily due to construction robustness.

 

[Gary RV_Wizard]

First of all, it's not the voltage that makes a difference. It's the battery design & construction. The 6v batteries referenced here are GC2 "golf car" deep cycle type, designed for frequent and heavy discharge & recharge. Other 6v battery type would perfrom differently, but that's not important here. There are 12v batteries designed the same way as the GC2 6v, for example the GC12 from Interstate, the US Battery US12VXZ, or the Trojan 30H. For a given amount of amp-hour capacity, those 12v batteries will perform just as well and as long as the GC2 6v models. However, they typically cost more per amp-hour.

But if you compare a 12v marine or automotive battery to a GC2 6v, you will see a difference in performance and life. Those batteries are not designed for frequent & heavy discharge, so don't last as long in typical RV use.

However, RVers who near-always connect to shore power will rarely (if ever) deep-discharge their batteries. Their battery power usage is actually much like a typical car and they can often utilize 12v marine or auto type batteries. And those types of batteries are usually relatively low in price.

I've written & published an article on lead-acid battery choices for RVs that explains the pros & cons of battery options without getting into a lot of techy stuff. There is a copy in the RVForum Resource library at RVForum - Choosing a battery

 

[Kirk]

He said that he did it after original 6V batteries finally gave up, and he found himself in a situation were 6V batteries were not available or be prohibitively expensive, so he downgraded to 2x12s as, he said, they are offering similar performance, but give much more flexibility, easier to source, and cheaper than 6Vs...

To put it in simple terms, when you change from 4 batteries to 2 batteries you only have half of the capacity for power, approximately. To actually compare it requires a lot more knowledge of exactly what the original 6V batteries were and what the current 12V batteries are. While you connect 2 batteries of 6V in series to get a combined 12V out, you still have twice as much in battery plates which is what stores the current. If you compare 2 batteries of 6V in series power capacity to that of 2 batteries of 12V in parallel, the total amount of power they can supply will be very nearly equal. The physical size of a flooded cell battery plays a major role in its capacity to store electrical power. You would be hard pressed to find a 12V battery anywhere that would have as much capacity as 2 series 6V batteries.

 

[Gary RV_Wizard]

You would be hard pressed to find a 12V battery anywhere that would have as much capacity as 2 series 6V batteries.

Right, It would have to be a size 4D 12v, which is essentially two 12v batteries molded into one casing.