6 volt vs. 12 volt

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IBTripping

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I need to get one or more deep cycle batteries for my TT. I've learned a lot researching this forum about battery use & care for dry camping. While I do most of my own maintenance/repair, I don't know much about DC. My question: Does a 6v 100AH deliver the same amount of service as a 12v 100AH battery for operating RV electrical devices? I'm finding a 6v costs less than a 12v.

 

muskoka guy

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One thing for sure, is you have to buy at least two batteries if you go the 6 volt route. 2 x 6 volts = 12 volts. Your system is 12 volt, so at least two sixes are required to make 12 volt. I think the main thing is the 6 volt are true deep cycle batteries, and are designed to do many more charge and discharge cycles than standard batteries.
 

kdbgoat

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One 12 volt true deep cycle battery will give you the same power as two volt batteries, but amp hour for amp hour, the two 6 volt will be less expensive. Look in the library (tab above), there is a great article about choosing an RV battery written by Gary the Wiz
 

IBTripping

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Thanks muskoka guy. And, yes, I'm only plan to purchase true deep cycle (not marine) batteries like those used in golf carts. If I decide to go with 2 of the 6 volt 100AH connected to have a 12v 200AH system.

Going that route would be less expensive than 2 of the 12 volt 100AH batteries. However, maybe someone else can tell me if a 6v 100AH provides that same service as a 12v 100AH deep cycle battery. If it does, then I'll go with 2 of the 6v 100AH batteries.

I only downside I can see is if one of the 6v goes bad, I can't use the remaining 6v as a backup. But, my TT already has a 12v 35AH battery which should keep me in service until I can replace the bad 6v. (I know I can't connect a 12v to a 6v battery.)
 

IBTripping

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kdbgoat said:
One 12 volt true deep cycle battery will give you the same power as two volt batteries, but amp hour for amp hour, the two 6 volt will be less expensive. Look in the library (tab above), there is a great article about choosing an RV battery written by Gary the Wiz

Thanks!!!
 

Lou Schneider

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What kdbgoat said is technically true, but what is overlooked is an individual golf cart battery will likely have around 200 amp-hour capacity, not the 100 amp-hours found in a similar sized 12 volt battery.

When you combine two of either type, you'll get 200 amp-hours of total capacity.  Series connected batteries (6 volts) add their voltage while the amp-hours stay the same as a single battery so you wind up with 200 amp-hours at 12 volts.  Parallel connected batteries (12 volt) add their amp-hours while the voltage stays the same so you also wind up with 200 amp-hours at 12 volts.

The advantage to using a pair of 6 volt batteries is the series connection ensures all of the charging and discharging current flows through all of the cells, as there is only one path through the batteries.  This keeps all of the cells evenly balanced and prolongs the performance of the battery as it ages.

12 volt batteries have a separate current path through each battery.  As they age, one battery usually starts doing less work than the other, degrading the performance of the pack.  A bit of corrosion on a connection or unequal battery wire lengths can also upset the delicate balance between the batteries.

The other advantage to using a pair of 6 volt batteries is they have half as many cells as a pair of 12 volt batteries (6 vs. 12 cells).  If the total amp-hours of the pack is the same, each 6 volt cell will be twice as large as a 12 volt cell.  Bigger is better in deep cycle use, allowing thicker plates and more rugged cell internal structures.
 

John From Detroit

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That is a complex question

6 Volt are generally GC-2 class batteries like my Deka G-20's these are actually 200+ amp hours when placed in series for 12 volts.. (Actually they are 200+ amp hours. but when you put 2 of 'em in series you get 12 volts at in my case 230 amp hours)

They are also DEEP CYCLE Batteries designe to be discharged as much as 50 percent and recharged over and a over and a over again.

Most 12 volt batteries are MARINE/deep cycle and should not EVER be discharged to 50 percent  75-80 minimum and State of Charge.. So

Now 12 volt at 100 amp hours woudl be a Group 29 or 27 (They both fall in that range)

Two Group 29's in parallel  Likely about the same total capacity as a GC-2 pair in series.
But you can only use 1/4 of it, as opposed to 1/2 on the GC2

And as you noted the GC-2 are often cheaper

WHY are they cheeper?  THousands and thousands of golf cars use 'em. Golf courses buy them in pallet size lots... Cars (Automobiles not golf cars) Well some days it seems there are a thousand different batteries so the plant produes a thou or two and then re-tools and then they produce a thou or two and they retool

With the six volt line it just runs and runs and runs and runs.

 

Lou Schneider

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John From Detroit said:
Two Group 29's in parallel  Likely about the same total capacity as a GC-2 pair in series.
But you can only use 1/4 of it, as opposed to 1/2 on the GC2

Not true.  Both batteries use the same internal chemistry, so you can discharge either one to half of the total amp-hour capacity.  Makes no difference if they're a pair of 12 volt batteries or a pair of 6 volt batteries.
 

Optimistic Paranoid

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Lou Schneider said:
12 volt batteries have a separate current path through each battery.  As they age, one battery usually starts doing less work than the other, degrading the performance of the pack.  A bit of corrosion on a connection or unequal battery wire lengths can also upset the delicate balance between the batteries.

Well, what you've said is true, IF you hook your positive and negative connections up to the SAME 12 volt battery in the pair.  If you hook the positive connection to one battery, and the negative connection to the OTHER battery, you won't have that problem.
 

John From Detroit

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Lou Schneider said:
Not true.  Both batteries use the same internal chemistry, so you can discharge either one to half of the total amp-hour capacity.  Makes no difference if they're a pair of 12 volt batteries or a pair of 6 volt batteries.

Chemistry yes. Plate construction is DIFFERENT. actually so is the chemistry but that's a bit beyond what I want to research today.  The lead plates are not pure lead they are an alloy and the alloy changes between Starting and Deep Cycle.  Off hand i do not recall the name of the chemical (Starts with an "A" as I recall) that is different.

Here is an article
https://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html
 

Gary RV_Wizard

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The advantage of the 6v GC2 golf car battery is that is a relatively inexpensive true deep cycle that can survive many deep discharges.  The common 12v battery sold in most stores is not a true deep cycle (despite the words Marine/RV deep cycle" on the side) and has about half the life span of the GC2.  You can get 12v true deep cycles, e.g. Trojans, but they will cost double what the GC2's typically sell for.

I suggest you read my article on RV Battery Choices in the forum Library at  http://www.rvforum.net/miscfiles/Choosing_right_battery.pdf
 

Gary RV_Wizard

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I think John is mixing up depth of discharge with the number of discharge cycles

Both true deep cycle and hybrid deep cycles have the same depth of discharge characteristic because that is driven by the lead-acid chemistry. The true deep cycle plate design difference yields a larger number of deep discharge cycles before the battery is toast.  With any lead acid battery, discharge below around 50% level shortens the lifespan significantly.  With a hybrid deep cycle, the plates can handle discharge down to the 50% level maybe 300 times, whereas the true deep cycle plates can handle a 50% discharge 2x that.
The net is that you get to use about half the rated amp-hours whether hybrid or true deep cycle, but the true deep cycle will keep on doing that 2x or more as long.
 

Kevin Means

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One suggestion if you decide to go with 6 volt batteries... Measure your battery compartment/case before you buy them. 6 volt golf cart batteries are taller than most 12 volt batteries, and they won't fit in some RV battery compartments (Like ours)

Kev 
 

IBTripping

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Here's what I've found doing some research in the library and other places. I'd have to use a pair of 6v batteries hooked in parallel to make it 12v for my TT. But, a pair of 6v with 100AH each, hooked in parallel would only produce 100AH; not 200AH. However, one 12v at 100AH would would cost less than a pair of 6v.

But, if 6v gets more cycles than a 12v, the long term cost would be less. (So glad I didn't choose to be an accountant.)

I did a search for golf cart batteries on Amazon and found there are 12v batteries that claim to be true deep cycle batteries. Here's an example of a 12v 35AH: Mighty Max Battery 12V 35AH SLA Internal Thread Battery Kangaroo TG-31 Golf Cart Brand Product - https://www.amazon.com/Mighty-Max-Battery-Internal-Kangaroo/dp/B06ZZPYBM6/ref=sr_1_10_a_it?ie=UTF8&qid=1540235304&sr=8-10&keywords=golf+cart+batteries+12+volt

I also found 12v 100AH batteries which are used for solar and TT applications. Example: Mighty Max Battery 12V 100AH Battery Solar Wind DEEP Cycle VRLA 12V - https://www.amazon.com/dp/B00S2MDZFK/ref=psdc_389574011_t3_B00S1RT58C

With the growth of solar applications, I'm wondering if more manufacturers are producing 12v true deep cycle batteries at a lower price than Trojan.
 

Lou Schneider

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IBTripping said:
Here's what I've found doing some research in the library and other places. I'd have to use a pair of 6v batteries hooked in parallel to make it 12v for my TT. But, a pair of 6v with 100AH each, hooked in parallel would only produce 100AH; not 200AH.
It might be easier to look at how much power is stored in the battery.  Power is Voltage x Current (in Amps or Amp-Hours) to give Watts or Watt-hours.  Your home utility charges you by the Kilowatt-hour, or 1000 watt-hours.

What you're missing is a 6 volt battery of similar footprint to a 100 amp-hour 12 volt battery will have 200 amp-hours capacity at 6 volts, not 100 amp-hours.  6 volts x 200 amp=hours = 1200 watt-hours.  Put two in series and you'll have 12 volts x 200 amp-hours, or 2400 watt-hours.

However, one 12v at 100AH would would cost less than a pair of 6v.

And only store half as much power as a pair of 6 volt batteries - 12 volts x 100 amp-hours = 1200 watt-hours.  You'll need two connected in parallel to equal the capacity of a pair of 6 volt batteries of similar physical size.

I added "of similar physical size" because some people will cite an example of a 12 volt battery that gives the same amp-hour performance as a typical 6 volt battery.  They exist, but they're twice the size and twice the weight as a similar amp-hour 6 volt battery.
 

RVMommaTo6

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This is like reading a different language. I'm trying to follow along, but I understand sooooo little of this. I'll have to see what kind of batteries I have. I assume all this info is for the auxiliary batteries and not the driving battery, is that accurate?
 

grashley

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Amanda, 
This discussion is about replacing COACH, or TT batteries, not the chassis or motor starting battery.  In short, starting batteries are designed to give a SHORT burst of HIGH AMP power.  Deep cycle batteries are designed to give long, steady, low amp power.  Kinda like comparing a fire hose to a soaker hose.  Both deliver water, but in a very different manner for a very different purpose.

This discussion is much more important for folks who routinely boon dock - camp without shore power.  Honestly, other than the educational value, for you, it is much ado about nothing until you have a battery go bad.  Then start a new thread and we will walk you through YOUR situation.

The one big point is that lead acid batteries are not designed to drain completely, then recharge, like a LiCad battery.  They are designed to deliver no more than half their rated capacity before recharging.  If you are normally on shore power, the converter keeps the battery charged all of the time.

Hope this helps!
 

RVMommaTo6

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Thank you! I'm going to be doing boondocking for about a week at a time while we're on our big trip so I'm trying to learn as much as I can to be prepared. I have 2 batteries, but I don't know anything about them (like if I need to add water to them like I've read on other posts)  I'll take pictures this weekend.
 

John From Detroit

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No I'm not mixing Depth with number

Starting batteries. Take 'em down to half (or less) and recycle them (Put in a new one)

MARINE/deep cycle.. MIGHT recover from a "under 50%" or not. but do well at a minimum DEPTH of 25% or 75% soc.. I'm not sure how many cycles.

But the deeper the discharge. teh fewer re-charge cycles you get.. They are not confused. they are related. DEEP CYCLE are designed to go down to 50 percent over and over

The rest don't like 50 percent at all. they like to be much fuller.

FOr all. if you go too low you do serious damage to the overall life (Number of recharge cycles).
 

IBTripping

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Lou Schneider said:
It might be easier to look at how much power is stored in the battery.  Power is Voltage x Current (in Amps or Amp-Hours) to give Watts or Watt-hours.  Your home utility charges you by the Kilowatt-hour, or 1000 watt-hours.

What you're missing is a 6 volt battery of similar footprint to a 100 amp-hour 12 volt battery will have 200 amp-hours capacity at 6 volts, not 100 amp-hours.  6 volts x 200 amp=hours = 1200 watt-hours.  Put two in series and you'll have 12 volts x 200 amp-hours, or 2400 watt-hours.

And only store half as much power as a pair of 6 volt batteries - 12 volts x 100 amp-hours = 1200 watt-hours.  You'll need two connected in parallel to equal the capacity of a pair of 6 volt batteries of similar physical size.

I added "of similar physical size" because some people will cite an example of a 12 volt battery that gives the same amp-hour performance as a typical 6 volt battery.  They exist, but they're twice the size and twice the weight as a similar amp-hour 6 volt battery.

I think I'm getting a better understanding of 6v vs. 12v. My TT is a 12 volt system. To use 6v I'd need at least a pair wired in series which equals 12 volts. But, according to Karl Kolbus in the library: "We mentioned earlier that some RVs might come equipped with two 6-volt batteries.
Unless it is a very, very old RV (think 1940?s), we can be pretty sure that they are wired in
series to produce twelve volts. The positive (+) terminal of the left battery is connected to
the negative (-) terminal of the one on the right. Again assuming each battery is capable of
outputting 100 ampere-hours, you might think that the total capacity would be 200Ah, but
that would not be correct. When batteries are wired in series, only the voltages of the
individual batteries are added together (6 + 6 = 12 volts), not their capacity. The capacity
remains at 100Ah
." (Emphasis added).

I don't understand why a pair of 6v 100AH each, wired to produce 12 volts, only has 100AH. But, I don't need to know why. What's important to me is that one 12v 100AH battery costs less than two 6v 100AH batteries. Either option gives me only 100AH. And, as the Kolbus article notes, if I have more than  two 12v batteries, I'll need to connect them in parallel so I don't end up shooting 24v into my TT.
 

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