Want to add more house batteries, need advice.

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SargeW

SargeW

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The new Journey came with 2 12 volt deep cycle batteries as house batteries. They have been working fine, but I would like to increase the size of the bank. For usual campgrounds and state parks the 2 batteries have been OK, but we will be getting into more "rustic" places as we head north with an eye on Alaska this summer.  My current batteries are Napa group 31 deep cycle, and have been in use about a year.  It seems that it would be cheapest to add two more group 31's to the bank to make 4.  I thought about going the 6 volt route, but cost wise the two 12's are going to be less of a hit than the 4 6's that I would buy. Fortunately space is not an issue in this rig, as one bay is dedicated to just my batteries.

And do the new group 31's need to be from the same manufacturer? Napa's are about $125 each. I think I can do better at Sams Club. 

Ideas or advice?

Sarge
 
Sarge, you'll get the best advice from us "battery bigots" if you can list the various AH ratings of the various batteries being considered.

My rig came with 2-6Vs, so the additional ones were also 6Vs, but I have no really deep founded preference for either.
 
Thanks Porky, I checked the batteries for their amp hour ratings, but it was not listed as such. This is what was on the battery label. CCA @ 32* is 810. CCA @ 0* is 650. The reserve capacity is 185. I went to Napa's web site and checked the model# of the battery #8231, but it only listed the above info. No AH ratings were indicated.  What is your take on it?
 
The reserve capacity of 185 means the battery will maintain voltage for 185 minutes with a 25 amp draw.  It won't still be 12v+, obviously, but it should still operate appliances requiring 12v at the end of that test.  I can't remember the exact formula for translating Reserve Capacity to Amp Hours, but I think it's about 105-115 AH for that battery.

Not a bad battery, in my opinion.
 
Well, so long as you stay with the same TYPE (IE: FLooded wet cells, or Maintenance free) you can mix six volt pairs with 12 volt batteries,, Just so you know.

Two G-31's will give you SLIGHTLY more amp hours than a pair of GC-2's

Just remember, There are no six volt batteries in RV's    Why do I say this?

When you put two six volt in series you have just made ONE 12 VOLT battery, size extra large.

And you can parallel 12 volts of different sizes... Just keep 'em the same chemically
 
RC is roughly double the AH. That's a rule of thumb, not a formula.

A better Group 31 deep cycle would give you much more AH or RC. For example, the Trojan Group 31 deep cycle produces 130 AH or 225 minutes of RC.

But you are right - the most cost effective solution is adding two more 12v, and "best practice" is to use two more identical to what you have.  Hard to say how adding two different 12v  would affect things, but when you cable batteries together they should be a close as possible in their electrical characteristics. Different brands and models of  batteries may or may not be similar - witness the Trojan example I gave. Definitely NOT similar in characteristics. How much different and what long term effect that might have, is anybody's guess.
 
Sarge:

Something else to consider. New motor homes usually have the batteries mistreated through production and sitting on a dealer's lot; lot's of discharges and recharging.

Adding two new batteries to your current ones will draw the new ones down to the charging level of the originals which makes insuring that your present ones are still in good shape a good idea.

 
All very good points guys. Jeff you are also spot on with your advice. In my 06' MH a "maintenance free" starting battery blew up in the middle of the night due to excessive off gassing when the rig was only about a month old. The health on my current pair seems to be pretty good.  They have held up well when dry camping and take a full charge fairly quickly.

Gary, I had not considered that possibility of different internal components in the different batteries. Here http://www.napaonline.com/Search/Compare.aspx?R=NBE8231_0056217521+NBE8231_0213555633+ is the link to my current battery make up. It is the most informational page I could find on their web site.

The difference between their battery and another manufacturer may be difficult to gage.
 
BTW Dan, I have seen that page before, and I believe it to be excellent information. Surprisingly, Winne has wired my current two to match the illustration in method 2. If I do add the additional batteries I will keep to method 2 as it makes a lot of sense to me.

In a previous thread on this site last year, I "hop scotched" my 3 house batteries after testing them with a digital volt meter. I found that the battery closest to the connecting cables was a few tenths of a volt weaker than the battery farthest away. In that set up Winne had both connecting cables on the same battery. I don't know if it would make a difference what the battery positions were if I had 4 batteries and used the preferred hook up in method #2.
 
SargeW said:
I don't know if it would make a difference what the battery positions were if I had 4 batteries and used the preferred hook up in method #2.
Click to expand...

maybe put your older batteries in the middle?
better yet, buy some extra cables and use hookup example #4.
 
I've never driven to AK but I've driven from Ankorage to Denali several times and the number of big diesel trucks is impressive.  I believe that they use 12V Gp 31's... both sealed starting batteries and wet deep cycle batteries.  Not that many golf cars I would guess.  On that basis alone I'd be tempted to stay with the ones you have and add two more 12V deep cycle NAPA's.  If you have any trouble, seems like there would be replacement batteries available along the way since there are so many big trucks.  Especially if you have been happy with two so far.  The roads are going to be rough on the batteries, and everything else I guess, so you could switch to 6V GC2's next time.  BTW, the GC2's are quite a bit higher, especially with some terminals so double check the clearances...  Watch out for the Eagles... they love to snatch little dogs and cats.
 
DAN L said:
maybe put your older batteries in the middle?
better yet, buy some extra cables and use hookup example #4.
Click to expand...

The furthest I go, in the balancing effort, is to use the same length and size cables in multiple battery banks that I intend to parallel.  In the RV environment, with all it's other variables, I don't see the payback for more effort or expense than that.  JMHO
 
Yeah, at this time I think I will stay with the flooded 12volts. Battery height is not an issue in this coach. I have the height of an entire bay to work with.  I think that you are right lou, I will keep the cables the same size and tie them down good.  I was able to find out that I have a 80 amp charger that recommends a 400 AH max battery bank.  That should do me just fine......
 
SargeW said:
. Battery height is not an issue in this coach. I have the height of an entire bay to work with.
Click to expand...

The opening in the sheet metal just inside the bay door was the limit on our Itasca.  I could have made the opening larger but I would have had to cut the sheet metal.  Once inside there is plenty of height.  As it turned out I had about 1/2" using GC2 batteries.  I guess yours is different.
 
It is a lot different. Here is a pic of my battery bay.  I actually added a shelf above it to use some of the extra space!
 

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SargeW said:
It is a lot different. Here is a pic of my battery bay.  I actually added a shelf above it to use some of the extra space!
Click to expand...

Yes, very different!  We have two trays that slide out, barely room for 4 GC2's in the top tray.  Looks like you could go to 3 extra deep cycle 12V Gp 31's.
 
DAN L said:
how you connect multiple batteries in a bank makes a difference.
http://www.smartgauge.co.uk/batt_con.html
Click to expand...
That was very interesting reading.  As I got half way down the page I got to thinking that one continuous chunk of electrical cable connecting all the batteries with the charger load connection in the middle would be a solution, although a pain to make up and work with, but the bottom solution is very interesting.
 
Well, as it turns out all the figuring about weather to keep the original batteries was a moot point. I pulled them out and put them on a bench charger to test the health of each battery. One of them is very weak. So now adding two more of the same would be a waste of money and time.

So I went down and bought 4 GC2 6 volt golf cart batteries from Sams. $72 a piece was not awful.  But now I have to put then in.  I have a wiring diagram for the 4 battery set up, but I have a question. When I had the 12 volt set up, the hook up was easy. I had 2 pos cables coming from the rig. One from the charger I assume, and the other to carry the juice to the rig.  Now with the 6 volt set up wired in series, what is the best way to duplicate the cables coming from the RV? 

Just a long jumper from one set to the next set? 
 
You are merely making a 12v battery from a pair of 6vs, then connecting the resulting two 12v in parallel. The wiring to/from the coach doesn't change from what you have now. The positive on one 12v/6V pair is the coach positive connection point and the negative on the other set is the ground (negative) connection point. Sounds simple, but its probably as clear as mud!  This subject is covered rather nicely in the late Karl Kolbus' library article on adding batteries. See http://www.rvforum.net/miscfiles/batterycon-1.pdf

The series jumpers between the two 6V's in each pair should be as short as possible, allowing for practical considerations (getting batteries in/out).  No need to skimp on a few inches for extra convenience in maintenance, but avoid extra feet of wire if possible.
 
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