Options for replacing 6 volt batteries

[Svenska]

It' been a very long time time since I was last on the website .....Busy year

My husband has asked me to throw this questions out to all of you for him,
and since I had no idea what he was talking about let alone how to pose this question, he wrote:

"Our cabin circuitry is 12 volt running off 2, 6 volt deep cycle
batteries.
If I were to replace my two 6 volt deep cycle batteries wired in series
with two 12 volt deep cycle batteries wired in parallel, would there be
any problems caused by this set up?"

Thanks in advance everyone for any advice you can give.  I will pass it on to him....

 

[Ned]

No problem in doing so, but there is little to be gained.  Why is he considering this change?

 

[Svenska]

Good question.....I'll ask him and get back to you

 

[John From Detroit]

Only one that I can think of..  COST.

You see, due to the size of the production runs 232 amp hour six volt batteries are kind of less expensive than 120 amp hour 12 volt batteries.

That one I'm sure of and you can easily see for yourself by visiting the battery store.

There are those who argue about battery chemistry and the ability of the true deep cycles to recover from an "OPPS" (which is better than the marine/deep cycle 12 volt types) but that argument tends to be long and hard

The $$$ argument is clear, you can find out for your self,  Oh, one word of caution

OPTIMA.. is 3/4 the battery at 4/3 (or 4/2) the price

 

[Svenska]

Thank you John.  I was just getting ready to reply to Ned.
That is exactly the reason why he wants to do it. 
Buy gas in order to travel or buy $$$$ batteries......that too is clear even if it is a bit of an exaggeration.
Thanks for the responses

 

[Tom]

Optima is only one option. I recently compared my new 4 x 6V golf cart batteries with a friend's new 3 x 12V deep cycle batteries (not Optima), and price per AH capacity was close to the same.

 

[John From Detroit]

Tom are you saying the 12 volt deep cycles were as expensive, per watt (or amp hour) as the optimas. or that the 12 volt deep cycles were as expensive per amp hour as the sixes?

I have found 12's are usually more expensive and Optima more expensive still

Optima is not, as far as I'm concerned, an option in all but the roughest service enviorments

In a wave runner or 4-runner.. perhaps

In an RV which we like to drive smooth and gentle.. NO WAY

 

[Gary RV_Wizard]

Tom, were his 3 x 12v the same total amp-hours as your 4 x 6v's?   Does not seem likely, based on the AH specs I see on 12v flooded cells in the Group 29 & 31 sizes (about as large as they get without going to a 4D or 8D size). I can see how 3 of one equaled 4 of the other in cost, but if the AH aren't the same...

On the other hand, my 4 x Group 31 12v AGMs cost about the same as 4 x 6V AGMs and yield about the same AH, so at least there it does not appear that there is any savings to be had.

 

[Tom]

Two weeks have gone by, and I can't recall what happened yesterday. I'll get the numbers and re-post. These were not 8D; I have 4 of them on the boat, along with 10 golf cart batteries, so I'm familiar with the differences.

The term 'watts' has no meaning in terms of battery capacity or charge without a time component.

 

[John From Detroit]

Well, we normally say amp hours when talking about batteries,  amp hours times voltage = watt hours

But frankly watts is a unit of work, for example so many watts of energy will heat a pound of water one degree F. 

NOTE that 1 amp of current flowing through a one ohm resistor for one hour will heat a pound of water one degree F

 

[Tom]

Well, we normally say amp hours when talking about batteries,  amp hours times voltage = watt hours

Agreed John, but this is the first time I recall you've used a time component when using "watts". Save the rest of the lecture; I have a EE background, although school was a long time ago.

 

[Gary RV_Wizard]

When talking about the inverter application, it would be handy of batteries were rated in watt hours rather than amp hours. As John says, the conversion is simple if you just assume an average of 12 volts. Using watt-hours, it is simple to comprehend how the 120vac loads, which are rated in watts, drain the 12vdc battery.

While I consider myself well-versed in battery lore, it was still enlightening to compute that a typical 90 AH 12v deep cycle contains only about 550 watt-hours if you stick to the recommended limit of a 50% discharge.

 

[Tom]

Watt hours yes, but watts are meaningless when used to state battery capacity, which was my earlier point to John.

 

[Svenska]

Thanks guys.  You always amaze me!
I am, however, staying out of the conversation after my hubbie told me last night that I read your responses bass ackwards! :-\
So funny...as I said, I know nothing about the subject.
He needs to join RV Forum!
Thanks guys

 

[Ned]

As I said in my original reply, there is little to be gained by going from 6V to 12V batteries.  In most cases, there is nothing to be gained.  Usually the simplest answer is the best

 

[Tom]

Agreed Ned, up to a point. We have four 6V batteries on the coach and 10 of them on the boat and, in each case, I considered them to be the best option for me. OTOH when I recently replaced the group 31 cranking batteries on the coach with sealed batteries, I realized I had 12 fewer cells to check and top up. I'd replaced the four 6V batteries on the coach at the same time but, when I saw 12V sealed deep cycle batteries on a friend's coach, I was thinking that could have been another 24 fewer cells to check. So, in that sense, sealed 12V would really have simplified things for me.

 

[Ned]

With sealed batteries, there are no cells to check, but that's irrelevant to the 6V vs. 12V decision.  The original question was regarding possible $ savings by switching to 12V batteries, and the answer is there almost always is no savings, and may actually cost more.

 

[Tom]

Sorry, I merely responded to your "Usually the simplest answer is the best" comment. Not having to check electrolyte in a bunch of cells would be far simpler for me. Nowt to do with voltage.

 

[Ned]

Right answer, wrong question   No wonder people get confused, even me.

 

[John From Detroit]

Well the bottom line is tihs

Baring a heck of a sale, or some special needs situtations (Such as it's very hard to access the batteries for watering) you get the best bang for your buck wish Six Volt.

Now I have seen cases were even Optima, which normally I'd never suggest, due to the fact you get less battery per cubic foot

But I've seen 'em at what amounted to "Here, Haul it away for me" prices.  (Wish I'd been there to haul a few) and at that price you can't ignore them.

But normally,  Your best price per performance is with sixers.  And that is due to the size of a six volt production run


That's the good news

The bad news is they now make golf carts that use 12 volt batteries.. So,,  sixers may, in a decade or two, start going up in price and 12's come down.  Plus we will see more TRUE DEEP CYCLE 12 volt in sizes we can reasonably wrangle.    But I'd not hold my breath waiting for that (See "Decade or two")