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Old 07-26-2011, 08:04 AM   #1
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Time to replace the batteries???

So on our last camping trip we realized that our batteries were not working properly. So i took them out and put them both on chargers. After being on the charger for two days i took them off and put them on the meter and realized that one of the two batteries had a bad cell. So now i have to replace both of them even though only one went bad but I'm not sure which way to go.

I have been looking at carquests NGT Extreme Batteries. They are an AGM Deep cycle style battery part number NG31 & NG34M both are made by Deka.
the NG31 has a reserve capacity of 190 and the NG34M has a reserve capacity of 120. the stock batteries only have a reserve capacity of 100



So both batteries would be better then the stock interstate batteries. My only problem is that the battery tray is to narrow for the NG31 so if i wanted to keep the battery tray i would need to stay with the NG34M but if i took out the tray and only used the battery box i could use the NG31 but then would need to find a way to secure them so they didn't push to door open on the side of the camper while traveling.

the NG31 cost's $230ea and the NG34M $157ea
we do a little bit of dry camping each year but we also have a Honda generator that we take with us when dry camping so I'm nor sure it is worth the extra expense of $145 for the NG31's over the NG34M's

And I'm not sure its worth going with two 6V batteries ether because i don't think i would have a reserve capacity higher then just buying two NG31 for a total reserve capacity of 380

So is it worth spending the extra money to have two NG31 for a reserve capacity of 380 or should i just save the cash and buy two NG34M's and keep the battery tray and have a reserve capacity of 240 which is still better then the stock interstate batteries that had a total reserve capacity of 200 together.

here is some pictures of the battery box

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Old 07-26-2011, 01:27 PM   #2
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You'll probably get best bang for the buck by getting batteries that fit from a reputable retailer who stands behind what he sells and offers a good warranty.

For a better available energy capacity measure to use for comparison, use 12 watts per pound of battery (AGM's maybe 10). Then figure that any differences less than 20% are insignificant.

See Sean's analysis and comments for an interesting set of numbers. Note what he says about batteries being commodity items.

Brand, type, small variances in size and other esoterica aren't going to make that much of a difference in the overall scheme of things.
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Old 07-26-2011, 02:01 PM   #3
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the NG31 cost's $230ea
Battery Capacity: 100Ah 20HR
Approx. Weight: 65 lbs
Dimensions (+/- 1/16 inch): 13 x 6 3/4 x 9 1/2 inches

so for available energy capacity you would take 10x65=650

the NG34M cost's $157ea
Battery Capacity: 55Ah 20HR
Approx. Weight: 41.5 lbs
Dimensions (+/- 1/16 inch): 10 3/4 x 6 7/8 x 8 3/8 inches


so for available energy capacity you would take 10x41.5=415

so that would be a difference of 235 per battery is this what you are trying to say?

Also if it helps here are the dimensions of our battery box with and without the tray

WxDxH with tray
12.75x13.75x11

WxDxH without tray
13.5x16x11.5

Is there another battery that you would recommend that would fit in the tray and have more capacity?
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Old 07-26-2011, 02:47 PM   #4
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Personally I really like Interstate - Just on a bang for the buck and national warranty reason. The GC-2 (U2200) is the workhorse of the RV market. It is a true Deep cycle - it is not even rated for cranking like the one that is in there now. It is only a .25" wider than what you have, slightly shorter but about 1.75" taller. They are inexpensive, found everywhere, dependable and for a motorhome - a perfect solution. Likely it will fit in the box without too much modification. My bus does not have a tray.
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Old 07-26-2011, 02:56 PM   #5
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Quote:
Originally Posted by CraigAllegro View Post
Personally I really like Interstate - Just on a bang for the buck and national warranty reason. The GC-2 (U2200) is the workhorse of the RV market. It is a true Deep cycle - it is not even rated for cranking like the one that is in there now. It is only a .25" wider than what you have, slightly shorter but about 1.75" taller. They are inexpensive, found everywhere, dependable and for a motorhome - a perfect solution. Likely it will fit in the box without too much modification. My bus does not have a tray.
We have four of the U-2200's, they are 9 years old as of last month and still doing OK for our use. When they go I'll replace them with U-2200's again.
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Old 07-26-2011, 03:14 PM   #6
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Try Costco Golf Cart Batteries. I've had a pair for 2 years and they are as good, with the same specs as Trojans but 1/2 the price.
Here's something I cut and pasted from Consumer Reports:
____

Most auto batteries are made by just three manufacturers, Delphi, Exide, and Johnson Controls Industries. Each makes batteries sold under several different brand names. Delphi makes ACDelco and some EverStart (Wal-Mart) models. Exide makes Champion, Exide, Napa, and some EverStart batteries. Johnson Controls makes Diehard (Sears), Duralast (AutoZone), Interstate, Kirkland (Costco), Motorcraft (Ford), and some EverStarts.
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Old 07-26-2011, 04:41 PM   #7
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You are comparing a 65# battery to a 42# one. That ratio is about the same for cost, volume, and capacity. That's a BCI group 24 to a BCI group 31 size

Note also that the newer, fit in the box, batteries you are evaluating are only 20% higher in capacity than the old ones (although the 20 hour rate should be used rather than the RC, which is minutes at 25 amps: peukert could make a difference here)

re: "It is a true Deep cycle" -- watch out for this sort of marketing hype. There is no such thing when it comes to lead acid batteries. The trade-offs are cost, capacity, and 'ruggedness' and the size of those trade-offs is not all that much. No lead acid battery does well with deep cycling. All RV and auto lead acid batteries will handle a typical RV's cycle rate if properly used and maintained.

Keep in mind that the battery tray does more than just hold batteries. It is a corrosion barrier and assists in proper ventilation among other things.

The key, though, is that the current batteries appear to have had sufficient capacity for your needs and you have a good backup handy (the genset).

First question to answer for yourself is "why AGM?" yes they may last about 1 and half times as long as a wet cell but look at the cost difference. Is it worth the cost premium?

Then consider your usage. Is increasing battery capacity by even double really going to make a difference in how you use your rig? What about the typical variance in your use? What about that 50% depth of discharge goal? Yes, you need reserve but just how much, really?

As noted by Sean in the link I provided and illustrated by Rick, batteries are a commodity item. That is why getting your batteries from a reputable retailer who sells a lot to folks like you and stands behind what he sells is more important than 6v vs 12v or brand x vs brand y or the other minutia people really get going on about IMHO.
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Old 07-26-2011, 04:51 PM   #8
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Hold the Phone! Did I get accused of marketing hype?
A bit of education needed - There is a massive difference between a starting battery and a deep cycle battery.

Here is expert quote.


Starting batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).
Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need. Although these an be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge.

Unfortunately, it is often impossible to tell what you are really buying in some of the discount stores or places that specialize in automotive batteries. The golf car battery is quite popular for small systems and RV's. The problem is that "golf car" refers to a size of battery (commonly called GC-2, or T-105), not the type or construction - so the quality and construction of a golf car battery can vary considerably - ranging from the cheap off brand with thin plates up the true deep cycle brands, such as Crown, Deka, Trojan, etc. In general, you get what you pay for.

Marine batteries are usually a "hybrid", and fall between the starting and deep-cycle batteries, though a few (Rolls-Surrette and Concorde, for example) are true deep cycle. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. It is often hard to tell what you are getting in a "marine" battery, but most are a hybrid. Starting batteries are usually rated at "CCA", or cold cranking amps, or "MCA", Marine cranking amps - the same as "CA". Any battery with the capacity shown in CA or MCA may or may not be a true deep-cycle battery. It is sometimes hard to tell, as the term deep cycle is often overused. CA and MCA ratings are at 32 degrees F, while CCA is at zero degree F. Unfortunately, the only positive way to tell with some batteries is to buy one and cut it open - not much of an option.
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Old 07-26-2011, 05:09 PM   #9
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Two Trojan 6 volt golf cart batteries will have a 225 AH rating of which you should only use 50% for battery longevity.
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Old 07-26-2011, 05:10 PM   #10
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"we do a little bit of dry camping each year but we also have a Honda generator that we take with us when dry camping so I'm nor sure it is worth the extra expense of $145 for the NG31's over the NG34M's"
You seem to have answered your own question. We seldom dry camp now(medical reasons), so I decided it is better for us to just install two 12V marine batteries(2nights dry camping power). We carry our Boliy 3600 generator with us anyway, so why spend money needlessly.
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Old 07-26-2011, 08:01 PM   #11
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re: "A bit of education needed - There is a massive difference between a starting battery and a deep cycle battery."

OK, show me the objective data that someone is willing to put their money on, like specifications, cost or warranty, that clearly indicates the difference.

I do understand that manufacturers make batteries aimed at specific market segments or use profiles. I don't suggest ignoring that focus (and a reputable retailer also won't intentionally sell batteries not intended for the proposed service).

But the reality is that there just isn't any 'true deep cycle' lead acid battery.

I know there is a lot of talk, a lot of 'expert' pronouncements, a lot of appeals to authority and such but the facts - the actual measurable data - speak much louder.

And, please, don't get into esoteric batteries but stick to what us common RV types can find in the market intended for our rigs.

The range of cycle life in the lab runs from about 200 to maybe 800. This is for discharging to 20% state of charge and then recharging. Going down to only a 50% SoC more than doubles the cycle life. Getting to the typical RV use profile cycle depth doubles that or more again. Compare that to the number of weekends in a typical 5 year battery life and see what cycle life does to crimp the typical RV lifestyle. Then we can start to get into the end of life indicators for a battery and how the typical RV enthusiast determines such a state.

Again - look at the hard data. Don't fall for terms with vague definitions not supported by solid measure. Don't get hornswoggled into spending money that won't get you anything (unless of course that is what you want to do).
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