Thinking of battery type/style change, need opinions

[FIRE UP]

Ladies and Gents,
Many of you have read my post on my latest issue with our new to us, Itasca 36GD, "Dimensions 2000" watt inverter and over heated batteries. Well after all the cleanup and making sure all the cables etc are in fine shape, I'm still finding one cell of one of the three (15) month old Interstate SRM-29 12V Deep Cycle Marine/RV batteries to be at 1.100. All the rest float from 1.225 to 1.300. Now most of you would agree that if, you're going to replace a battery in the house bank, you should replace ALL THREE CORRECT????

Well, as stated, these are only 15 months old and we're not the original purchasers. The warranty is for 30 months but, there's a tag on each of the batteries that states the warranty is for the ORIGINAL purchaser ONLY!

So, at this point, we haven't even camped one day in this rig yet and I'm faced with the possible purchase of 1, ONE new SRM-29 to compliment the other two that are in what appears to be OK shape or, 2, buy (3) new SRM-29 12v units because that's the supposed "correct" way to do it or, 3, and here's my choice, (1) 4DM battery to replace all three. Now, if you look in the accompanying charts, you'll see some specs for the 4DM that are far and above the SRM-29. But, even though the specs are above the SRM-29, THERE ARE THREE of the SRM-29s in the tray.

So, since I'm a bit rusty on the rating of batteries and groups of batteries, could someone enlighten me on just what would be a more sensible choice here. And yes, I'd like to go with the U2200 6V Golf cart batts that I had in my Bounder but, I'd need (4) and I don't have the room in the tray. The 4DM sure looks and sounds like the way to go. Has any one done that? Thanks for reading this.
Scott

P.S. I tried to copy and paste the chart from the interstate website but it would't past correctly and it was incredibly hard to read so, at this time, if you would simply go to the Interstate battery web site and type in 12V Deep cycle battiers and then click on specifications, you'll see the chart I'm referring to. Sorry I tried to do the work for you but, it's not happening.

On edit: here's a link to the chart;
Marine/RV Specs

[KIX]

I checked the Interstate site hoping to see the AH (amp hour) rates for the two battery models yo mention. The only rating I saw was 675 CCA (cold Cranking Amps) and 1314 CCA for the SRM29 and 4DM battery respectively. So, with only that info it's difficult to say with certainty but IMHO you'll have more usable AH with the 3 SRM29's than a single 4D.
And if it were me I would replace the one bad SRM29 and go camping.

[RJay]

I agree with KIX. You could probably get 5 to 6 years out of that bank if you replace just the bad one. When it comes time to replace the batteries put the largest batteries that will fit in the space available, whether that be 6 or 12 volts. That should give you the most amp/hrs you can carry.

[FIRE UP]

Well Guys,
I too looked for the "amp/hour" rating and could find it on the U2200 6V units I had in the Bounder but, could not determine what it is on the SRM 29 or the 4DM. I just like the fact that the 4DM has a lot more in reserve minutes etc than the SRM 29. But, that's why I ask here, to learn. We're not heading out too soon 'cause we're still loading, moving, re loading, adjusting, etc. The Bounder had a ton of room and I thought I had less in this newer D/P but, it appears I've got tons of room. So, I'll be on the hunt for battery while we're finishing loading her for our first trip.
Scott

[skigramp]

Have you thought about removing the bad battery and go with the two good batteries until you make your decision? ... that way the weak battery will not drag down the other two ...

[RJay]

Looking at the Interstate specification sheet, the 4DM is not a pure deep cycle battery but a 12 volt deep cycle/start battery and has a RC@25A of 390 amps with no amp/hrs listed.


To compare apples to apples the U2200 is a pure deep cycle 6 volt battery and has a RC@25A of 474 and 232 amp/hrs. IMHO you would be better served with two U2200 rather than one 4DM.

[wa8yxm]

First, Ignore Cranking amps ratings, they are meaningless save for starting batteires.

As I recall a 4D (pages are loading now) is a bit more than 2 G-29's. Less than 3, when it comes to Amp Hours. that's one of the factors you need to consider.

The other is battery type.. For house batteries you want DEEP CYCLE, not Marine Deep cycle, Not starting, (Which re the cranking amps) but DEEP CYCLE which are the amp-hour types)

now for the record, for any give size, sve for the Optima brand they all hold about the same amount of power (Optima holds less) but the level to which you can safely discharge is lower with the Deep Cycle types.. About 50%

I was able to find (on my hard drive) figures for the G-29 that confirm about 100 amp hours (20 hour rate) Your links were useless, one was for G-24 batteries (About 73 amp hours each) and the other did not load period.

But it's all amp hours. USABLE amp hours, That and warranty are the only real considerations. You might look at pairs of GC-2 batterires, See if you can fit two pair. Each pair (These are six volt batteries when you are carrying them so you always buy pairs) Each pair is a 12 volt, 220 amp hour, DEEP CYCLE battery. Two pair gives you 220 amp hours of usable power.

[FIRE UP]

Gents,
I emailed Interstate direct and received a reply fairly quickly. Although the Customer Service Rep that contacted me said my plan for changing to a "4D" would work, he did send along an Interstate booklet in PDF form that explains all about Interstate batteries and battery terminology. It's a nice bit of information. But, one thing I didn't see in it was whether on not you "add" the A/hours together if and when you have a bank of 6V units or not.

That is, if you have, like I did on my older Bounder, (2) U2200, 6V batts, do you add the amp/hours of each one together, making 460 amp/hours? Or, is it that it's still 230 amp/hours each, just for longer? huh? Where's the Aflac duck when you need it? The booklet didn't explain that.

And by the way, yes sir, I don't pay attention to the "cranking amps" 'cause they really only apply to engines for starting etc. I would set up (4) U2200 6V units but, I don't have the room and I can't figure out how to get the tray out so I can make room. It seems it's welded in there. So, for now, I think I'll just get a replacement 12V unit like what I've got in there or, head over to Walmart and see what they've got like one of you suggested.

Yes, we do "boon dock" about 95% of the time so, we need the staying power of multiple batteries. Thanks again to all of you for taking the time to answer and help here.
Scott

[POPPASMURF]

All this is nicely answered on the Trojan Battery site. As I remember you do not add the amp/hours for 6 volt batteries in series, but you do with 12 volt batteries in parallel. That is why I went with 3 -12 volt batteries of 200 amp hours each. (Trojan)