Battery question

NOTE You do not add capacity when wired in series, you add voltage

To lessen confusion, would it not be clearer to state "amp hours"? "Capacity" can certainly be expressed as watt hours which is "storage" -- another less ambiguous term than capacity.

Some of this stuff is hard-to-grasp by folks lacking aptitude.

Voltage PRESSURE

Amps FLOW

Amp Hours ENERGY STORAGE BASED ON TIME

Like putting height markers on a water tank indicating HOURS. Measurement is calibrated by the size of the drain pipe.

Very tall skinny tank (high voltage less storage) offers fast flow but less time flowing

Squat large tank offers low flow pressure but for for a looooong time.

Cells in series are tanks stacked one atop another -- vertical pressure buildup

Cells in parallel are tanks placed side by side. Lower flow. less pressure

Storage is amp hours is gallons -- nothing else.

No this analogy isn't by any means perfect -- but it beats hard to comprehend terms (at least I hope so)

Hi 2oldman,

But I do follow your links!

I learn all the time--sometimes even from new questions that are phrased in a different way making me reevaluate my answers.

The points to consider.
First two six volt batteries connected together in SERIES = one BIG 12 volt battery.. and when properly installed (IN SERIES) that is what they are.

THERE are THUS no six volt batteries in RV's.. just 12 volt that are spit into 2 pieces for ease of handling and installation. Think of them this way and many questions get answered (IE: Do I have to change my inverter.. NO you don't since you still have a 12 volt system. though you may wish to adjust more on that later)

Next: The most common type of 12 volt battery in an RV is "Multi-Purpose" that is MAREINE/deep cycle or MARINE/rv. MARINE means it is a starting battery raded for Cranking amps (32 degrees and above) but not COLD craking amps (ZERO F).

deep cycle (lower case) Means next to nothing.... These batteries need to be maintainwed at 75-80% State of chargem going lower causes rapid aging... Going very low.. they MIGHT recover but do not count on it.

A full Starting battery is about the same with teh exception of the word MIGHT, they do not often recover, rare enough to say they won't.

A DEEP CYCLE battery such as a Golf Car battery (GC-2, what do you think the GC stands for??) is designed to go down to half full (50% state of charge) and stands a fairly good chance of recovery if it goes lower but is promptly re-charged.... Mine did several times over 9 years and the replacewments have once (Converter died).

Some capacity ratings, Remember for MARINE/deep cycle or MARINE/rv you can only use 20%

Group 24, about 75 AH
Group 27 95
Group 29 105
Group 31 130

GC-2 (You can use half) 220 give or take 10 (my first ones were 215 and my new ones 230) NOTE You do not add capacity when wired in series, you add voltage

Finan comments: Due to the large number of golf cars in the world (Think of all the golf cars that follow the president around Mar-A-largo) the lines that make these batteries basically do not shut down and re-tool This means lower per unit cost. So this is the battery that gives you the most BANG for your BUCK.

It is thus what I recommend.

Now on inverter adjustments.. Some invereters you can set the capacity of the battery this affects the maximum charg rate when it is in charge mode.

A pair of Group 24's would be 150 amps.. You may wish to dial it up to 200 or 210 for a pair of GC-2's.. I would suggest a bit light.. Mine was set to 400 amp horus but I have over 500 amp horus of battery in this house.

old guy wrote:

" but we will answer each question as if the guy who asked is new to the rv life or has been around as long as I have and that is rving since the 60's."


Maybe tomorrow someone will ask the same question we'll do it all over again, and I'll post the same links that won't likely be read.

SoundGuy wrote:
because those who've taken the time to respond in recent days or weeks to similar discussions are much less likely to type their thoughts on the subject all over again so soon after, the result being far fewer responses to the query.

It's like we have a library that gets burned down every night. Some people have a distinct need to be told a story rather than read.

jalichty wrote:
My batteries are reaching the end of their good useful life and I am wondering whether to replace them with two 6 volt rather than two 12 volt ones?

SoundGuy wrote:
Oh boy, here we go again on a subject that was already recently discussed to death. :R

old guy wrote:
yes it has been discussed many times but so has winterizing and unwinterizing and tires and tow bars and toads and which MH to get and what tires to buy and which truck is best for a 14K 5th wheel. but we will answer each question as if the guy who asked is new to the rv life or has been around as long as I have and that is rving since the 60's.

Sentence structure has also been around a long time as well old guy ... why not try it? :W

As for the OP it's always a good idea to first screen recent discussions to see if what you want answered has already been addressed and heck, there's even a SEARCH function right at the top of the forum page where you can't miss it that makes this SO easy. :) In fact, anyone who posts a question without first doing a quick search is only doing themselves a disfavour because those who've taken the time to respond in recent days or weeks to similar discussions are much less likely to type their thoughts on the subject all over again so soon after, the result being far fewer responses to the query. The SEARCH function is there for a reason, not just for show - do yourself a favour and use it. ;)

SoundGuy wrote:

jalichty wrote:
My batteries are reaching the end of their good useful life and I am wondering whether to replace them with two 6 volt rather than two 12 volt ones?

Oh boy, here we go again on a subject that was already recently discussed to death. :R

yes it has been discussed many times but so has winterizing and unwinterizing and tires and tow bars and toads and which MH to get and what tires to buy and which truck is best for a 14K 5th wheel. but we will answer each question as if the guy who asked is new to the rv life or has been around as long as I have and that is rving since the 60's.

My post was not advocating the use of LCO batteries. Why are you implying that?

pianotuna wrote:
GordonThree,

Why do you not like LiFePO4?

The key advantage of LiFePO4 batteries is safety ! I would not want a large bank of LiCo batteries in my vehicle (Boeing made a big mistake with this on the 787). LiCo batteries require much more sophisticated monitoring.

GordonThree wrote:
Mostly lower nominal and working voltages
Discharge voltage of 2.5 ... A lot of energy is left on the table unless you can set your low battery cut out down low enough.

Inverter companies need to change their thought process. For a small amount of addition money they could design an inverter that would run of of 6 LiFePO4 cells (15V nominal) and not turn off until <10.0V.

jalichty wrote:
are they worth the additional money?

?????? less money

pianotuna wrote:
GordonThree,

Why do you not like LiFePO4?

GordonThree wrote:
I was marveling at some cells designed for forklifts, 8ah per cell rated for 200a continuous discharge. They were LiFePO4 chemistry though, which I'm not crazy about.

Mostly lower nominal and working voltages
Discharge voltage of 2.5 ... A lot of energy is left on the table unless you can set your low battery cut out down low enough.

Lower energy density is a concern too


Image from batteryuniversity.com

NMC offers the same energy per kg as the "dangerous" lithium cobalt cells, but with safety similar to LFP