6V vs 12V batteries for solar system

[boondocking]

Originally Posted by babock

Not if they are the same manufacturer and type! A Trojan 12V golf cart battery is the same as the 6V GC battery

If they are both deep cycle, then the comparison is the same.
What we are discussing here is deep cycle 6V compared to standard 12V (starting or dual purpose) batteries.

[CincyGus]

I have two of these 12v deep cycle golf cart batteries.

https://www.trojanbattery.com/product/t-1275/

Gives me 300 Amp Hrs at the 20 hr discharge rate (which is generally what is quoted on other batteries) with 150 usable. When I go full time in a few years I'll upgrade to Lithium but for the time being, these do just fine and give me plenty of usable energy for long trips with the inverter running the fridge until I can run the genny to get them charged back up.

[tomkatb]

The statement of 6’s being able to charge more often is from the Trojan site.

While both batteries 6 & 12 volt have the same warrantee, their literature said the 6’s will take substantially more. Got to read all the literature.

If you discharge a new 12 and a pair of 6’s 100% the amps available is higher the second time on the 6’s. Internet video I watched.

In the past golf carts always used 6’s.

Has to do with cell sizes I think. Not my area of expertise.

I also have one of the rare cars with a pair of six volt batteries. They seem to last 7-8 years easily. In my sailboat the 12’s never lasted three years. I seriously abused them!

[babock]

Originally Posted by tomkatb

The statement of 6’s being able to charge more often is from the Trojan site.

From the Trojan site, the number of 50% charge cycles is identical between 6V and 12V batteries.

Hard to even find a golf cart that uses 6V batteries anymore. Since almost all are 48V, they use 4 12V in series or 6 8V in series.

[SlowrideHD]

I have sixteen of the T-105 Trojan 6 volt batteries in a solar setup (off grid cabin). 8s-2p setup. That's eight in series for 48 volts, then another eight in series. Then the two banks in parallel. Float voltage is generally around 53.2 volts. Have about 3,320 watts of solar with good sun.

I fully agree that the specs on Trojan 12v and 6v are comparable when you add up the amps/volts. The difference that I have experienced is that for me, the 6v have required far less maintenance than when we were using a 12v bank. I can't say the conditions were exact because the 12v system was all parallel and required extremely heavy cables to prevent volt loss in the runs.

That being said...I've sort of went against my own experience because in my current camper, my battery bank is 12v parallel. But that is because I sort of got out of sequence with replacing battery's at the same time (had a bad cell in a 12v and only replaced the one). If I ever replace the bank in there now, I'll go with the 6v Trojans.

[mnoland30]

It is difficult to find true deep cycle 12volt batteries. When you do, they are very expensive. I got two 6v golf cart batteries (true deep cycle) for about $89 each at Costco. They may give you more than you need, but during a rainy week, that is a good thing. I bought a Harbor Frieght tapered tool box for the front of the trailer to put them in. I had to move the propane forward an inch or two. I now have some tool storage in front, and am less likely to have batteries stolen.

Be aware that there are lots of transient voltages in an RV. Disconnect your batteries from the trailer when in storage. Then the solar will keep them charged up forever. Just to be clear, you do need a charge controller. I have a 100 watt panel mounted to the top of my trailer. Works like a charm.

[babock]

Originally Posted by mnoland30

It is difficult to find true deep cycle 12volt batteries.

It's actually simple. I can drive less than 20 miles and have 3 sources of Trojan 12V batteries. They have pallets of them. If you have golf courses nearby, there are golf cart dealers that carry them. I just helped my friend put 4 of them in his Yamaha golf cart.

[tomkatb]

Costco sells the 6 volt batteries for less than $100. Similar to the t-105

6 volt vs 12

It would appear that there is no significant difference in capacity and voltage between these two examples. But this really is not the case. The plates designed for the T-105 use the same active material and alloy of the group 27 deep cycle batteries but both the T-105 negative and positive plates are 60% thicker than those found in the deep cycle 27 group sizes. The significance of this is that these 6 Volt batteries should have a longer lifespan than the two deep cycle 27 group sizes, if properly cared for. While the capacities are similar (220 versus 225 Amp Hrs.), battery longevity favors the two 6 Volt batteries. Why? Because a major cause of deep cycle battery failure is the shedding of active material from the battery plates.

If you cannot afford Lithium then two six's are likely the best deal.

Cell size sort of makes a battery more durable to abuse.

[babock]

Post a link that shows plate thickness

BTW, if the plate thickness actually makes a difference, shouldn't the plate thickness of the 6v be 100% bigger than the 12v since it has twice the current going through it.

Back when I worked for GM and worked on the EV1, we used lead acid batteries in the beginning. Guess what voltage batteries were used...yep...12v.

Originally Posted by tomkatb

Costco sells the 6 volt batteries for less than $100. Similar to the t-105

6 volt vs 12

It would appear that there is no significant difference in capacity and voltage between these two examples. But this really is not the case. The plates designed for the T-105 use the same active material and alloy of the group 27 deep cycle batteries but both the T-105 negative and positive plates are 60% thicker than those found in the deep cycle 27 group sizes. The significance of this is that these 6 Volt batteries should have a longer lifespan than the two deep cycle 27 group sizes, if properly cared for. While the capacities are similar (220 versus 225 Amp Hrs.), battery longevity favors the two 6 Volt batteries. Why? Because a major cause of deep cycle battery failure is the shedding of active material from the battery plates.

If you cannot afford Lithium then two six's are likely the best deal.

Cell size sort of makes a battery more durable to abuse.

[ScottBrownstein]

Originally Posted by babock

Post a link that shows plate thickness

BTW, if the plate thickness actually makes a difference, shouldn't the plate thickness of the 6v be 100% bigger than the 12v since it has twice the current going through it.

Don't see why it has twice the current...Battery has more AH, but 6 v is 6v. Now, if it did have twice the current, shouldn't the plates be 400% bigger????

But, I have been up since 2AM, so my mind might be failing...

[babock]

Originally Posted by ScottBrownstein

Don't see why it has twice the current...Battery has more AH, but 6 v is 6v. Now, if it did have twice the current, shouldn't the plates be 400% bigger????

But, I have been up since 2AM, so my mind might be failing...

Let's say you have a 20A load. In a series setup each of the 2 6V batteries has 20A through them. In a parallel setup with 2 12V batteries, each 12V battery has 10A.

[ScottBrownstein]

Originally Posted by babock

Let's say you have a 20A load. In a series setup each of the 2 6V batteries has 20A through them. In a parallel setup with 2 12V batteries, each 12V battery has 10A.

OK, I see where you are going. Your example is true but installation and multiple batteries is really outside the purview of the battery design. Both currents are within the design parameters of the battery. Hard to design for a bunch of aftermarket installation strategies...with the exception of 6 in series for golf cart applications. Sure there are a lot of solar, marine and RV applications but a hell of a lot more golf carts.

[babock]

Originally Posted by ScottBrownstein

Sure there are a lot of solar, marine and RV applications but a hell of a lot more golf carts.

I have been golfing for just 10 years now but I have not come across a single golf cart that uses 6V batteries anymore. All are 48V these days so they only use 8V or 12V batteries. I have a lot of friends that own their own golf carts too and helped them replace their batteries....no 6V.

[Jay2504]

When I got our golf cart, I chose 36volt so I could replace 6-6volts with 3 12volts and save weight in the truck bed. I know it hurt the range, but the way we use it, it hasn’t caused any problems. Jay

[babock]

Originally Posted by Jay2504

When I got our golf cart, I chose 36volt so I could replace 6-6volts with 3 12volts and save weight in the truck bed. I know it hurt the range, but the way we use it, it hasn’t caused any problems. Jay

You must have an old golf cart. If you go to the EZGO site, you can't even buy a 36V golf cart anymore. Only 48V and 56V and the 56V are lithium.

The future for golf carts is lithium. If I was like some of my friends that moved to a golfing community, I would only buy a lithium powered golf cart.

[Flat_twin]

Not much to add to whats already been said. Our local golf cart dealer had a great price on Crown batteries. These are HEAVY! Did a lot of boondocking last summer with limited generator hours per campground rules at times. Also replaced the factory charger/inverter with a quality multi stage charger that should give us maximum life out of our battery investment assuming no total discharge accidents happen.

[skipatroller]

Originally Posted by Outsider

I'm currently designing and building a very moderate size solar backup system for our small (16 foot) travel trailer. I've done lots of research and reading but would appreciate your input on this battery question.

When using good quality batteries such as Crown or Trojan (golf cart type) units is there a real advantage of (2) 6V units in series as compared to (2) 12V units in parallel? (Honestly, one good 12V unit may be enough.) Does one give you more bang for the buck? Does one discharge more slowly or charge more quickly? Is the usable power storage greater on one that the other?

We are VERY conservative with our power usage which will be primarily 2-3 DC interior lights, maybe 30-90 minutes of TV/DVD on a pure sine wave inverter every day or two, and recharge of a small SSD laptop every day or two.

Your knowledgeable input is desired. (No guessing please.)

I was in your spot last year at this time and this forum is very helpful, as long as you can decipher when the crazies respond with all there off the wall mathematical equasions.
I have a much bigger camper with a residential fridge to keep this short I made a bank of 4 6v. batteries was the best way to get the highest amp/ hour rating. I have 2 banks of the 6 volts in series, I also installed a battery selector switch so I can do either bank separately or both at the same time, I dd this so I'm never without any power, when 1 bank goes down I can just switch over to the other. I also upgraded to AGM batteries, it is a battery that is more forgiving if you drain it down to far, yes a little bit costlier on the front side but your supposed to get better life out of them.

[CJM]

Originally Posted by camaraderie

A pair of Group 31 batteries from a quality mfr. can provide just about what a pair of 6V will in terms of amp hours. THEN the real test becomes HOW MANY CYCLES to 50% discharge can I expect. If one battery offers 500 cycles and another offers 1000...then the longer lived battery is TWICE the value of the other assuming the price is the same.
There is a BIG difference in cycle life between the cheap 6V OR 12V batteries and the various premium brands ...but the premiums come at a premium price so the el cheapo may STILL be a better buy.
The el cheapo 6V's in general are a better buy than the el cheapo 12V since the plates are thicker.
FWIW...If you are planning on doing a lot of boondocking...get a quality battery. I like 12V for one pair since if one fails in the boondocks...the other should still be good. Not so with 6V...yer dead in the water. For 4 batteries...I like 6V.
Above all...invest in true battery monitor like Victrons, Trimetrics or Balmar, It's a much better way to spend $150 bucks than on replacing a murdered battery.

Well said. There seems to be alot of misinformation on batteries here. The most important things to remember when choosing batteries are quality ( you get what you pay for), type ( AGM , GEL, STANDARD WET CELL, LITHIUM) and capacity ( Amp hours). There is no advantage to 6v over 12v, when comparing relative capacity, longevity and quality. 6v became popular as one of the first high capacity, deep cycle type batteries. They gained a reputation for longevity due to their large capacity vs. Standard car batteries, and as a true deep cycle, could handle handle the cycles as well as of course, the longevity. The best bang for tour buck batteries right bow are AGM. Great cycle ability, storage, longevity. But as always, research the quality factor before purchase.

I know everyone has an opinion, and I respect that. Some are based on what they were told, some their own experience. Mine is based on 26 years in the business with solar, batteries and installs. It's what I do.

Good luck

[correpat]

Our Class 3 came with two 12v batteries and they fit nicely, end to end, in the top entry step. We’re never been without enough power when boondocking, but there’s only two of us, we don’t watch TV and we’re conservative with our power usage. I’ve noticed the two 12v batteries charge fast. We prefer Trojans and we run Trojan deep cycle 6v batteries in our electric boat - great batteries!

[RStock]

Originally Posted by prairiecamper

I love the argument about 6 volt versus 12 volt batteries. The consideration that if you have 2 - 12 volt batteries in parallel and one fails you still have the other one.

So I have to ask the question, will you be there at the exact same time that the 1 - 12 battery is failing to separate them?? Because if you are not there very soon after, the other good 12 volt is going bye bye as well.

This is so true, but infrequent. With two 12v batteries in parallel one cannot monitor them individually, thus you really don't know which one is failing. And if one fails you must separate them immediately else you risk destroying the good one.

However, 12v battery reliability is very good. Think about how many car batteries you had to replace due to failure with all the vehicles you owned in your lifetime? Deep cycle batteries are much more reliable as they are designed to withstand two to three times the recharge cycle of a car battery.

Do what fits best in the space you have. However, the overall recommendation is to go with two 6v batteries and monitor each one.