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Battery price question...

kfp673
Explorer II
Explorer II
It's time to replace the single 12V we have on our trailer. We do boondock from time to time so I have been reading a lot on these forums about 6V vs 12V. My question here is, where are these inexpensive 6V batteries I keep reading about? When I read the 12V vs 6V discussions I always see someone say to use 2 6volts and you will get 200+ Ah and they are less expensive. I am not seeing that. Duracell and others I can find seem to be starting around $120 and going up for the golf cart battery which is the same price as many size 27 12V 100 Ah. Seems to me I could just buy 2 12V and have similar Ah. So I guess I am just not seeing the cost savings. What am I missing? Thanks
35 REPLIES 35

Veebyes
Explorer II
Explorer II
It is much more complex than simply what it on the price tag. It starts with your camping habits & how many AHs you can get into the battery space.

A solution seldom suggested is using a single 4D case sized battery. A 4D battery is about the same size as 2 GC6Vs & similar AHs. I imagine the weight is about the same as 2 6Vs. The small advantage is simplicity of cabling. No in series linking of cable to be monitored.

What is the service life of a 4D vs 2 6V GCs? I don't know. I use a 4D, but it is an AGM. Being an AGM opens a whole nuther can of discussion worms but my last AGM 4D gave me 9 very active years.
Boat: 32' 1996 Albin 32+2, single Cummins 315hp
40+ night per year overnighter

2007 Alpenlite 34RLR
2006 Chevy 3500 LT, CC,LB 6.6L Diesel

Ham Radio: VP9KL, IRLP node 7995

RambleOnNW
Explorer II
Explorer II
Gdetrailer wrote:

...
The big downside to parallel operation is not "everything" is "shared", due to manufacturing and material tolerances the batteries will never "share" the current load 100% equally, resulting in one battery discharging or recharging at a different rate. You can get them close but in the end one battery will be slightly weaker and that weaker one will ultimately kill the other battery by over discharging and undercharging.

The 12V batteries due to thinner and lighter plates are also NOT designed for very deep draw downs, typically rated at only 50% DOD but for max LIFE only 20% of their capacity should be used..
!


Variances between 12 volt batteries is corrected by doing a balanced connection, connecting the house + connection to the + terminal of one battery and the - house connection to the - terminal of the other battery, then running equal length connections between batteries:



I use 2 AGM batteries made by Northstar and they are rated for 400 cycles at 80% DOD and the cycle count goes up from there with lower DOD.
2006 Jayco 28', E450 6.8L V10, Bilstein HDs,
Roadmaster Anti-Sway Bars, Blue Ox TigerTrak

kfp673
Explorer II
Explorer II
Was back in my local costco and sure enough they started carrying the 6V again. I asked the guy working there why they had stopped and he was not sure but they had 10 in stock. Picked up 2 and am currently in day 3 of a boondocks trip as I type this. What a difference from my single size24 marine batt. Ha! Nights right now are ranging 37-42 so the furnace runs plenty over night. This morning the battery reads (at least according to my in command system) 12.1v which apparently is around 60%. My old 12v would have been totally dead by about 5am. I run my generators a few hours in the afternoon to recharge and so far so good. Time will tell but thanks again all. This will make boondocking life much easier!

bikendan
Explorer
Explorer
kfp673 wrote:
Thanks again all. This is great info so I appreciate the conversation!

I am pretty sold on 6V at this point as we do plan to boondocks more this spring / summer /fall than we ever have. I did more on-line digging and found the Sams club Duracell's at $89. Of course the nearest Sam's club is an hour away. Costco is our regular bulk warehouse at 10 min away and as stated mine has stopped stocking the Interstate. My in-laws have a Sams near them and a membership (again an hour from our house) so we will give it a shot next time we are down that way. Next challenge will be to find battery boxes that fit. Looks like a few nice ones on Amazon.

Thanks again all!


many Walmarts carry 6v GC2 battery boxes.
Dan- Firefighter, Retired:C, Shawn- Musician/Entrepreneur:W, Zoe- Faithful Golden Retriever(RIP:(), 2014 Ford F150 3.5 EcoboostMax Tow pkg, 2016 PrimeTime TracerAIR 255 w/4pt Equalizer and 5 Mtn. bikes and 2 Road bikes

pianotuna
Nomad II
Nomad II
Gdetrailer,

The thinner plates IMPROVE high amperage performance.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

kfp673
Explorer II
Explorer II
Thanks again all. This is great info so I appreciate the conversation!

I am pretty sold on 6V at this point as we do plan to boondocks more this spring / summer /fall than we ever have. I did more on-line digging and found the Sams club Duracell's at $89. Of course the nearest Sam's club is an hour away. Costco is our regular bulk warehouse at 10 min away and as stated mine has stopped stocking the Interstate. My in-laws have a Sams near them and a membership (again an hour from our house) so we will give it a shot next time we are down that way. Next challenge will be to find battery boxes that fit. Looks like a few nice ones on Amazon.

Thanks again all!

Gdetrailer
Explorer III
Explorer III
pianotuna wrote:
Gdetrailer,

All you have said is correct--but the REAL difference is that two six volts in series have 6 cells and two twelve volts in parallel have 12 cells. So the load per cell is 50% less with a pair of 12 volt cells. There are other factors too.


Piano, what you state has "some" merit, however with 12V batts to fit 6 cells into the case, you now have to REDUCE the size and amount of grids along with the amount of electrolyte within each cell. Parallel operation also means your interconnects can be lighter since they are only needing to handle half the current.

The big downside to parallel operation is not "everything" is "shared", due to manufacturing and material tolerances the batteries will never "share" the current load 100% equally, resulting in one battery discharging or recharging at a different rate. You can get them close but in the end one battery will be slightly weaker and that weaker one will ultimately kill the other battery by over discharging and undercharging.

The 12V batteries due to thinner and lighter plates are also NOT designed for very deep draw downs, typically rated at only 50% DOD but for max LIFE only 20% of their capacity should be used..

On edit, forgot to mention 12V batteries with smaller and less plates per cell, the internal resistance of each cell goes up.. Yep, in reality the 12V battery jars actually will have a higher internal resistance! You are only getting away with it working since your are paralleling and reducing the OVERALL internal resistance slightly but in doing so you have now limited the max draw down depth of discharge you can use..

GC2 batteries on the other hand with larger and thicker grids are designed from the ground up to handle extremely deep discharges, their life ratings are based on up to 80% capacity being able to be used..

20% usable capacity (12V marine) vs 80% usable capacity (6V GC2 pair) per pound and dollar 6V GC2s basically net you much more usable capacity for the money..

Obviously your situation is a bit different with whatever you are doing with a 3KW load (AC unit?) but in your case, if the internal resistance is bothersome to you, then the fix would be AGM GC2s (extremely low internal resistance)or if you have the room 4 FLA GC2s setup in two series pairs that are paralleled. That combination would give you far more usable capacity than 8 12V group 27 Marine batteries..

For my situation, so far, have never had my inverter shut down or go into alarm during my home fridge startup and that is at a min of 100A surge and by morning the batteries have been drawn down to 50% of capacity.. I don't see any "advantage" to swap to 12V batteries as that would mean I would need to add at least 4 if not 6 more 12V batteries to the mix. That is a lot of money and weight that I am not needing to add to the trailer..

The big key is USABLE capacity for the cost!

Boon_Docker
Explorer II
Explorer II
Yes phlih, very minimal resistance. Would be hard to measure. 4g copper wire has a resistance of .284 ohms per 1000 feet.

pianotuna
Nomad II
Nomad II
Gdetrailer,

All you have said is correct--but the REAL difference is that two six volts in series have 6 cells and two twelve volts in parallel have 12 cells. So the load per cell is 50% less with a pair of 12 volt cells. There are other factors too.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

philh
Explorer II
Explorer II
you're only talking a few inches of distance. According to the charts, you don't need anything like 2 or 4g

Gdetrailer
Explorer III
Explorer III
pianotuna wrote:
mr_andyj wrote:
I cannot think of a single reason to use two 12 vs 2 6's.


High draw of 200 amps works much better on twin 12 volt batteries. I use a 3000 watt inverter, and I push it hard.


One of the issues is most folks skimp on the interconnect cables on 6V batteries, using too light of a ga of wire results in a pretty high voltage drop across that interconnect.

If you used standard automotive size cables as interconnects that is where the issue is. Typical automotive cables are 4 ga at best like THESE..

You might find some in 2 ga but 4 ga will be more common.

I used 1/0 wire as an interconnect and I have no issues with heavy startup surge loads from my home fridge conversion on the GC2 batteries even when the batteries are at 50% DOD.

The interconnect cable becomes part of the batteries "internal resistance" and the GC2s often get a bad rap for having a high internal resistance and some of that is most likely from using to low of a ga of interconnecting jumpers.

GC2s are a pretty darn hardy battery, they have to be as they were designed to be used all day on golf courses and that may mean more than 12hrs per day per charge so they tend to get worked extremely hard and deeply discharged but yet stand up to a full "season" of golfers..

DrewE
Explorer II
Explorer II
kfp673 wrote:

- I have not Checked wall-mart or auto parts stores. Where I have found 6V in stock local to me was a battery plus location selling Energizer, a golf cart company selling Trojan, and an interstate store. The price ranges for those 3 locations for a single 6V was $128 for Energizer / Interstate up to $200+ for trojan. NAPA online is $120. I am just not seeing anything below that. I was comparing that to a 90 Ah 12V Interstate for $120 each. This is where I came up with similar AH for similar money with 2 12V . 180 Ah with 12V vs 240Ah with 6V. By the way, we are fine paying a little more, I just wanted to make sure I was not missing something since I read so many posts talking about <$100 6V batteries.


A third again more capacity for the same price is not, in my book, "similar Ah for similar money." I suppose it's partly a question of perspective, what similar capacity means.

pianotuna
Nomad II
Nomad II
mr_andyj wrote:
I cannot think of a single reason to use two 12 vs 2 6's.


High draw of 200 amps works much better on twin 12 volt batteries. I use a 3000 watt inverter, and I push it hard.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

Gdetrailer
Explorer III
Explorer III
kfp673 wrote:
Thanks for all the replies. I have a few responses to comments made throughout these posts.
- To be clear, I am comparing 2 6V vs 2 12 v not a single 12v. I have room for either on my tongue
- The Costco option does not appear to be an option for me. My Costco no longer carries them. Said they can order but when you read on-line the reviews are horrible for that Interstate 6V battery.
- I have not Checked wall-mart or auto parts stores. Where I have found 6V in stock local to me was a battery plus location selling Energizer, a golf cart company selling Trojan, and an interstate store. The price ranges for those 3 locations for a single 6V was $128 for Energizer / Interstate up to $200+ for trojan. NAPA online is $120. I am just not seeing anything below that. I was comparing that to a 90 Ah 12V Interstate for $120 each. This is where I came up with similar AH for similar money with 2 12V . 180 Ah with 12V vs 240Ah with 6V. By the way, we are fine paying a little more, I just wanted to make sure I was not missing something since I read so many posts talking about <$100 6V batteries.
I had my mind set on going with 6V this time around but was just surprised on the prices as I had always head they are cheaper. And, I was very surprised to see such terrible reviews on the Costco website for the Interstate 6V. I do have a tendency to discharge the battery quite far when we boondock, especially if we have to run the furnace, so points made in this thread of deeper discharge might be the important focus point for our situation

Thanks again everyone. I know this topic is beating a dead horse, but it was the Value / Cost angle I wanted to look at here.


One has to be careful reading the reviews.

I toss out all the top reviews AND all of the bottom negative reviews and read the MIDDLE reviews.

Reviews are high subjective and that is a problem, one persons expectation of said item will be far different from someone elses expectation and there a lot of shill reviews on top of that.

Some folks also just abuse things and expect it to survive.. get mad when it doesn't and then writes scathing shill reviews..

YES, $90 GC2 batteries DO EXIST, however, that price may not be "available everywhere". Your not the first person that has showed up on this forum with this same issue.. I am a bit shocked because my closest city which is 20 miles away from me is so far in the dung heap for retail stores it isn't funny.. We operate on a Walmart, Target, Sam's club, a small grocery chain, Home Depot and Lowes, Tractor Supply and a Rural King.. The one large indoor mall that is still existing now has only 30% of its capacity used and those are little "one off" trinket stores..

But, yet, I can walk into my local Sam's club and right on the shelves IS those $90 6V GCs.

I can also walk into my local Rural King and buy their house branded Rural King GC2s for about the same price as the Sam's Club GC2s.

I am having a difficult time wrapping my head around the idea that you live in such a bad place (I didn't think anything could be worse than my area), sounds like you are in rural Vermont (yeah, been there, don't plan to go back, too expensive).. You are sure you live in PA?

Perhaps, broaden your search area and make a "daytrip" to a different Costco or if you know someone with a Sam's membership and are near a Sams club have them pick them up for you..