6 volt vs. 12 volt

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Lou Schneider

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Do what you want, just be aware that you won't find a 100 amp-hour 6 volt battery, which makes your interpretation moot.  6 volt batteries are typically 200 amp-hours each, meaning a pair wired in series will deliver 200 amp-hours at 12 volts.

Here are a couple of practical examples from the same source (Batteries Plus, a nationwide chain of battery stores).

First, a pair of 6 volt GC-2 deep cycle batteries:

Duracell GC-2 Golf Cart Battery

At $99 each, two six volt batteries will cost $198 for 12 volts, 225 amp-hours of storage.  That's 88 cents per amp-hour.

Next, a 12 volt, 105 amp-hour deep-cycle battery of the same brand, from the same source:

Duracell Group 31M 12 Volt Deep Cycle Battery

At $130 for 12 volts, 105 amp-hours of storage, it costs $1.24 per amp-hour.  While one of these batteries is three times as much storage as your present 12 volt, 35 amp-hour battery, you'll need two of these to approximately equal the capacity of a pair of 6 volt GC-2 batteries.

Your present battery is 12 volts at 35 amp-hours:

Duracell 12 volt 35 amp-hour battery

At 35 amp-hours of storage, it's considerably smaller than either of the above examples.  You'll need 6 of these to get the same performance as a pair of golf cart batteries, or 3 to equal the single 12 volt, 105 amp-hour battery.  At $90 for 35 amp-hours, it has a cost of $2.57 per amp-hour.

But note this is a maintenance free, sealed AGM battery.  The other examples are wet cell batteries, which require venting and occasionally replenishing the water levels.

The physical size and weight may also be a consideration.  The 35 amp-hour battery is 7.67"L x 5.13"H x 7.09" D and weighs 20 lbs.  Both the golf cart batteries and the 31M 12 volt batteries are considerably larger and heavier than this.

I hope this helps in your decision.
 

Gary RV_Wizard

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The least cost answer is a 12v Marine/RV battery in the Group 24 size. You can find them anywhere batteries are sold, even Walmart, for around $100. 

https://www.walmart.com/ip/EverStart-Maxx-Lead-Acid-Marine-RV-Battery-Group-24DC/139801236

The GC2 golf car batteries will supply more power and last longer (typically 6-7 years), so they are less costly over time even though you have to buy two upfront.
 

IBTripping

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Lou Schneider said:
Do what you want, just be aware that you won't find a 100 amp-hour 6 volt battery, which makes your interpretation moot.  6 volt batteries are typically 200 amp-hours each, meaning a pair wired in series will deliver 200 amp-hours at 12 volts.

Here are a couple of practical examples from the same source (Batteries Plus, a nationwide chain of battery stores).

First, a pair of 6 volt GC-2 deep cycle batteries:

Duracell GC-2 Golf Cart Battery



At $99 each, two six volt batteries will cost $198 for 12 volts, 225 amp-hours of storage.  That's 88 cents per amp-hour.

Next, a 12 volt, 105 amp-hour deep-cycle battery of the same brand, from the same source:

Duracell Group 31M 12 Volt Deep Cycle Battery

At $130 for 12 volts, 105 amp-hours of storage, it costs $1.24 per amp-hour.  While one of these batteries is three times as much storage as your present 12 volt, 35 amp-hour battery, you'll need two of these to approximately equal the capacity of a pair of 6 volt GC-2 batteries.

Your present battery is 12 volts at 35 amp-hours:

Duracell 12 volt 35 amp-hour battery

At 35 amp-hours of storage, it's considerably smaller than either of the above examples.  You'll need 6 of these to get the same performance as a pair of golf cart batteries, or 3 to equal the single 12 volt, 105 amp-hour battery.  At $90 for 35 amp-hours, it has a cost of $2.57 per amp-hour.

But note this is a maintenance free, sealed AGM battery.  The other examples are wet cell batteries, which require venting and occasionally replenishing the water levels.

The physical size and weight may also be a consideration.  The 35 amp-hour battery is 7.67"L x 5.13"H x 7.09" D and weighs 20 lbs.  Both the golf cart batteries and the 31M 12 volt batteries are considerably larger and heavier than this.

I hope this helps in your decision.

Lou, thanks for the info. Much better price than I found on Amazon. Fortunately, there is a vendor near me so I won't have to pay shipping. I'd prefer using a true deep cycle battery rather than marine. So, I'll start with a pair of 6v and add another pair if needed.

And, thanks to everyone else who commented. This discussion has been very educational and was a great help to me in making a decision on which batteries would best meet my needs.
 

kennyshark

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I put two 6V Interstates on my 26' Tracer, I bought the battery boxes from Amazon and the Batteries Local. Remember to keep distilled water on hand and check them at least once a month. I've had mine on since 2013 and They still work great.
 

Kennethh

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For those who are confused about choosing between 6 volt and 12 volt RV batteries for motorcycles and touring trailers, we offer these tips: Many 12-volt batteries on the market have an amperage of 50 Ah to 100 Ah. The average 6-volt battery on the market provides 225 amp hours, typically ranging from 160 Ah to 260 Ah. 6-volt battery systems have thicker and heavier plates that allow them to withstand the chemical changes inside the battery, so 6-volt batteries can be said to have a longer lifespan. But in terms of cost, 12-volt battery systems are inexpensive and available at most auto supply and battery stores.
 

IBTripping

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For those who are confused about choosing between 6 volt and 12 volt RV batteries for motorcycles and touring trailers, we offer these tips: Many 12-volt batteries on the market have an amperage of 50 Ah to 100 Ah. The average 6-volt battery on the market provides 225 amp hours, typically ranging from 160 Ah to 260 Ah. 6-volt battery systems have thicker and heavier plates that allow them to withstand the chemical changes inside the battery, so 6-volt batteries can be said to have a longer lifespan. But in terms of cost, 12-volt battery systems are inexpensive and available at most auto supply and battery stores.
This is an ancient thread which includes a naïve question by me when I first bought my TT. At any rate, I ruined one of my expensive 6 volts. Decided to change to one 12 volt. Got big 12 volt from Walmart with 122 amps for about $80. Works great even when the shore power goes out for several hours.
 

John From Detroit

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For those who are confused about choosing between 6 volt and 12 volt RV batteries for motorcycles and touring trailers, we offer these tips: Many 12-volt batteries on the market have an amperage of 50 Ah to 100 Ah. The average 6-volt battery on the market provides 225 amp hours, typically ranging from 160 Ah to 260 Ah. 6-volt battery systems have thicker and heavier plates that allow them to withstand the chemical changes inside the battery, so 6-volt batteries can be said to have a longer lifespan. But in terms of cost, 12-volt battery systems are inexpensive and available at most auto supply and battery stores.
I had no problem finding GC-2 Golf Car (6 volt Deep cycle) batterries. Sam's carries 'em Costco can order ''em most any golf course gets 'em by the truck load (Why they are low cost)
They are actually CHEAPER than 12 volt for the same capacity

What's more because they are DEEP CYCLE they can take an "OH C**P! level discharge and come back for more better than most 12 volt types.

That said you can get genuine 12 volt DEEP CYCLE batteries.. but they tend to be pricy because they are rare. Not as rare as they used to be (Check the GC-12) but pricey.

Another difference... Pound per watt hour (Amp hours times volts) most all lead acid batteries are within 10% or less of each other.. So 220 amp hours divided between TWO six volt jars is.. Something I can wrangle into/out of my motor home (And did) 220 amp hour 12 volt battery (4D) Forget about it.
 

Gary RV_Wizard

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I will once again offer the article I've written on this subject. It explains the choices (trade-offs) of the various battery options for RV house batteries. I've tried to keep it simple - most owners just want the lights to work and not require them to fuss with batteries all the time. The tech types already know batteries, so I didn't see the need to write for them.
RVForum - Choosing a battery
 

Ex-Calif

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It is simpler to understand when you use the math. Watts is the measurement of power

Volts X Amps = Power in watts

6V X 80 amps = 480W
12 X 80 amps = 960W

In a series circuit voltage is cumulative and amps are constant

6V + 6V = 12V X 80 = 960W

In a parallel circuit volts are constant and amps are cumulative.

(12 V X 80 = 960W) + (12 V X 80 = 960W) = 1920W

1920 / 12V = 160 amps

Deep cycling is important if you boondock a lot. Golf carts use 6V batteries because they are basically run flat each day.

I use 12V marine batteries because I don't deep discharge a lot ad I get more usable amps in the battery space available.
 

creativepart

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@IBTripping, you keep mentioning getting "2-6v batteries and wiring them in "Parallel" to get 12v."

That's not correct. you wire the 2-6v batteries in "Series" to get 12v.

Wiring in Parallel the voltage stays the same but the amp hours (wattage) double.

Wiring in Series the voltage doubles but the amp hours (wattage) stays the same.

Also, you won't find standard size 6v batteries configured as 100 amp hour batteries. They will be 200+ amp hours. So, two 6v 220aH batteries wired in Series will yield one 12v-220ah Battery Bank. (Series doubles the voltage, doesn't change the amps.)

Group 31-sized 12v batteries are typically 100ah. Two of them wired in Parallel will yield one 12v-200aH battery bank. (Parallel doubles the amps, doesn't change the voltage.)

With Series wiring the positive terminal of one battery is connected to the negative terminal of the other battery.

With Parallel wiring the positive terminal of one battery is connected to the positive of the other battery (and negative to negative, too).
Par-Series.png
 
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IBTripping

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creativepart I may have said that in 2018. But, I'm not going to go through this old thread to see what a I posted 3 years ago when I got my first TT.​

 

creativepart

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Sorry about that. I went through this thread from the beginning and saw you and others posting this past week. I should have noticed that the thread was old.

Bold text... nice touch.
 

Mooree

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I will refer to deep cycle batteries when talking about 6V or 12V batteries for RVs. The good news is that you can connect two such batteries in parallel to increase the amps to 100 Ah or 200 Ah. Connecting two 6-volt batteries in a series will meet the 12-volt electrical requirements of modern touring trailers, campers, motorcycles, and RVs. However, the amperage rating remains the same.
 

John From Detroit

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Now here is a question:
Why are a pair of 6 Volt 230 amp hour batteires so much cheaper than a 12 volt 230 amp hour:
Answer.. The GC battery class (think Golf Car) are purchased by the pallet load by Golf Courses from here to there and back again... Other formats of lead acid batteries still ship by the pallet load.. but not nearly as many pallets.
So re-tooling to make a different size (Expensive retooling) happens less, if at all.
 

Ex-Calif

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Now here is a question:
Why are a pair of 6 Volt 230 amp hour batteires so much cheaper than a 12 volt 230 amp hour:
Answer.. The GC battery class (think Golf Car) are purchased by the pallet load by Golf Courses from here to there and back again... Other formats of lead acid batteries still ship by the pallet load.. but not nearly as many pallets.
So re-tooling to make a different size (Expensive retooling) happens less, if at all.
It's all that plus making a 12V battery at the same capacity as a 6V battery is more challenging.

In general terms the discharge and charge rates of a battery are related to surface area of the plates. The durability of the battery is related to the robustness (thickness etc) of those plates.

When drawing a 10a load from a 12V battery you are drawing 120W. When drawing from a 6V battery you are drawing 60W. Intuitively one could argue, yeah but it's only 3 cells and to get 10a @12V from a 6V there is another battery with 3 more cells.

Sure but the heat and all is spread out across 2 form factors.

So if I am gonna draw 50amps sustained unless I have a lot of surface area the 12V vis-a-vis 6V will "appear" to discharge faster because of the battery chemistry and Peukerts law, which in one aspect says as the temperature goes up the discharge rate goes down.

The other aspect is the chemistry of the battery needs time to shift in the reactants. The "acid" ions and lead ions need to rearrange in order to continue to meet and make the reaction that results in current. If you shed those ions too fast there is no time for the ions to come from deeper in the lead plates or from the acid moving around.

That's the simplistic view based on my "self teaching" of battery physics.
 

Gary RV_Wizard

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Why are a pair of 6 Volt 230 amp hour batteires so much cheaper than a 12 volt 230 amp hour:
The same reason a 10 gallon bucket costs more than a 5 gallon bucket: the 6V is only half the capacity, storing 6v x 230 AH = 1380 watt-hours of electrical energy. The 12v battery is 12v x 230 AH = 2760 watt-hours of energy. The 6v is also half the physical size of a 12v with the same AH capacity - see Ex-Calif explanation of the lead plates. A 6v battery requires only 3 cells, while a 12v requires 6. Lead is actually quite expensive, so doubling the amount of lead plates (6 cells vs 3 cells) nearly doubles the production cost of the battery.
 

Mark_K5LXP

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and Peukerts law, which in one aspect says as the temperature goes up the discharge rate goes down.
Peukert constant, unless congress got involved. :) Just the opposite- batteries are a chemical reaction and the higher the temp the more efficient it will be. But at higher temperatures all the "bad" things happen faster too. Peukert is just a way to express battery efficiency in Ah vs current. It falls apart at very low and very high currents but for "practical" values it works out very close.

Mark B.
Albuquerque, NM
 

Ex-Calif

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Peukert constant, unless congress got involved. :) Just the opposite- batteries are a chemical reaction and the higher the temp the more efficient it will be. But at higher temperatures all the "bad" things happen faster too. Peukert is just a way to express battery efficiency in Ah vs current. It falls apart at very low and very high currents but for "practical" values it works out very close.

Mark B.
Albuquerque, NM

I'll just figure you are pulling my chain a little bit. I do recognize you have pretty strong feelings about your knowledge of batteries so rather than get involved in a full blown google war...

>>It is called Peukert’s Law. Peukert’s law expresses mathematically that as the rate of discharge increases, the available capacity of that battery decreases.<<

>>
Peukert’s law is tricky. It basically throws a wrench into everything you know about a battery’s amp-hour (AH) rating and, ultimately, how long your battery will last. After all, a 100AH battery should last either 100 hrs at 1 amp, 20 hrs at 5 amps, or 1 hr at 100 amps, right?

Not quite–and this is where the Peukert Effect comes into play. It mathematically explains how the rate of discharge influences the battery’s actual capacity. If you run your battery at a high rate of discharge, the internal resistance within the battery creates a voltage sag that ultimately shortens how long it will last.

This is the Peukert effect in a nutshell. <<

These are quotes from two pretty reliable battery makers. Bold highlighting by me.

I don't put myself out as a chemical engineer or physicist. The reactions are complex but I do know that high discharge creates high temps which limits available current potential.

Whether it's Peukert's Law or Peukerts constant it could be "The Peukert Effect" (according to the clip above) and we're both wrong - LOL...

I would postulate the the Peukert formula is not a constant because the exponent is variable.

>>The Peukert exponent, or k, will differ for each battery, but its value ranges between 1 – 1.6. The formula to determine the Peukert exponent is a little more complex–it looks like this:

k = (logt2 – logt1) / (logI1 – logI2) "

Finally I will post one real google result and that's Wikipedia because all the Wolrd's nerds would go nuts if Peukert's Law couldn't be called a law and Wikipedia says it is - LOL...

Peukert's Law According to Wiki
 

DonTom

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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?
A few facts that may help you understand a bit.

An "AH" in a battery is NOT always an AH. It varies under the current draw and often they rate them where they get the best AH rating.

An engine battery is designed for a very heavy load for a very short time.

A good house battery is the opposite, it's designed for low current draws but for a long time.

A so-called "Marine deep cycle battery" is between the two. Best to replace the word "marine" with "fake" if you want a decent house battery.

For a decent house battery, a trick that usually works is to make sure there is NO CCA (Cold Cranking Amps) or MCA (Marine Cranking Amps) rating at all.

That us because a decent house battery is NOT designed to start an engine--but usually still can do such if needed in an emergency. If they do have a Cranking amp rating, a decent one will have a poor rating, so they normally don't mention it.

I see the big advantage of six-volt batteries to be each one is a lot lighter than a single 12V of the same capacity. I too would take two 6-volt house batteries in series over a single 12V. They are very heavy-- heavier than an engine battery, so best to divide up the weight and save your back.

But it you really want a decent house battery; you need to go with a pricy lith. You get what you pay for. They have many advantages, and the only disadvantage is price.

If you do not boondock much, then even a marine battery will do just fine as a house battery. The more you boondock, the more you want to spend on a house battery/batteries.

-Don- Reno, NV
 
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