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Old 08-13-2008, 01:48 PM   #1
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Yet another battery question...

My wife and I recently acquired a used 2005 19' Bambi. Our first AS, and first RV as a matter of fact.

We've been out on three weekend trips so far.

Once we got it home and I started to figure out how 12v DC electricity works in RV's, I realized that the two batteries that came with it were in sad shape.

One battery was a wee bit low on electrolyte/water and the other one was low enough that 1/2-1" of the lead plates were exposed.

I charged them up using the Bambi's charge, by plugging it into shore power, and started the process of trying to nurse them back to health.

Ultimately I got a multi stage battery charger.

Ultimately I was able to get them charged to the point where my DMM reflected 12.57v testing the two together.

We went out last weekend. When we got back from our trip, we figured out where to go next month. The place we are going does not have electric hook up.

With that knowledge I actually wanted to test the batteries.

Here are my results.

7:10pm = 12.67v (likely high surface charge because we got home two hours earlier)
9:57pm = 12.36v
10:37pm = 12.35v
11:44pm = 12.33v
8:05am (next day) = 12.23v
A couple of days latter = 12.19v

This was the load on the battery. The CO detector and a MaxxAir Fan on level 2, which according to the manufacture draws 2.9amps.

In 12:05 (12.92) the batteries were drained 40% and for the sake of argument, 49amps. I have no idea what the CO detector draws or any other vampire loads on the batteries.

The batteries are Astro DP-24, and there is two of them. The batteries show their capacity at 23amp @140minutes.

We plan to change the batteries to deep cycle Type 27 or Trojan T-105, but we were hoping to wait until next season.

My question is, are my batteries doing what they are expected to do or are they not performing very and really need to be replaced?

I look forward to your responses!

Chris
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Old 08-13-2008, 03:00 PM   #2
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In my humble opinion, I would not go boondocking with those batteries. The last time we went, we ran one battery until the lights got dim and switched to the other.(I know this is not the suggested procedure). Anyway, we were able to go 2.5 days each, running the refrigerator electronics, a fantastic fan as needed (similar to your Maxxair), the water pump as needed, and lights at night. These add up to a lot more load than you describe in your test. These were run of the mill deep cycle batteries, approx. 3 years old.
Depending on the refrigerator, if the batteries die, the fridge turns off, even when running on gas.
I would spend the $60 each for a couple of deep cycles.
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Old 08-13-2008, 03:27 PM   #3
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The no/low load voltage drop from those batteries seems OK, but the sulphate on the exposed plates will likely reduce the capacity.

If you go boondocking a lot you should consider getting a good quality battery monitor (more than just a voltmeter) so that you know exactly where you stand on remaining power.

If you're considering T-105's, take a look at T-125's. You get an additional 20 A/h from a battery in the same size case. Also, remember that those are 6V so they have to be wired in series.
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Old 08-13-2008, 03:30 PM   #4
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Ever since I switched to (pricey) AC Delco "Voyager" batteries..problems zero.
All three batteries are going on their fifth year & test perfect, so they're not that
pricey when that's taken into consideration.
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Old 08-13-2008, 03:39 PM   #5
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What we don't know is to what extent they will charge or when they were last fully charged, which will take days with little or no load. Eventually you will want some sealed deep cycles with 200amps or so.
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Old 08-13-2008, 03:58 PM   #6
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Look in to AGM (absorbed glass mat) deep cycle batteries. I have found these to be the best there is. Your choice of manufacturer can vary (sort of like oil) but in all of the solar charging systems that we install where battery capacity and integrity is critical, we use the Lifeline GPL-6CT golf cart batteries almost exclusively (GPL-4CT where space is a concern) that are 6VDC and 300 amp hours. These have 'boondock' written all over them!
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Old 08-15-2008, 01:09 PM   #7
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Thanks for the thoughts...looks like I'm shopping for new batteries.

Cheers,

cgd
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Old 08-15-2008, 03:09 PM   #8
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we use the Lifeline GPL-6CT golf cart batteries almost exclusively (GPL-4CT where space is a concern) that are 6VDC and 300 amp hours. These have 'boondock' written all over them!
When you install these 6 volt batteries I assume they are in series and still charged by the 12 converter.

I have heard this suggestion before but have a question. How come a couple of 6 volt 300 AH batteries can out last 2 12 volt 800 hour batteries
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Old 08-15-2008, 03:53 PM   #9
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Generally speaking, most 12V. batts are designed for engine starting, where a lot of currant must be supplied for a very short period of time; To do this, the plates are thin, but great in number. In a true deep-cycle batt, the plates are fewer in number, but much thicker. All of the different types, ie. AGM, lead-acid, etc., have pros, and cons, with much debate over which is better/best. The 6V. deep-cycle types usually give better service in true deep-cycle conditions. Never an easy decision to make, as the opinions are as varied as the people making them. That said, heavier is usually better, for a given size. How's that for straddling the fence.
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Old 08-15-2008, 04:38 PM   #10
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When you install these 6 volt batteries I assume they are in series and still charged by the 12 converter.

I have heard this suggestion before but have a question. How come a couple of 6 volt 300 AH batteries can out last 2 12 volt 800 hour batteries
Comparing the life of different battery setups, is near impossible, unless you apply the same loads, the same drains, the same discharges, the same charging rates from identical chargers, the same highway bounces, the same water that is added, the same temperature exposures, and the same manufacturer dates, in the same exact order.

Probably only a full programed reseach project could come up with "what is best."

Short of that then goes back to opinions based on a particular persons personal experience, that does not contain any of the if's, and's or but's, or specifics, of any kind that could be duplicated, exactly.

Andy
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Old 08-15-2008, 04:59 PM   #11
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2x6volt in series

I used this set up for a period and found that overtime, one of the two batteries would not fully charge. Charging rate is determined by two factors - 1. the applied voltage and 2. the internal resistance of the battery. As the batteries charge, the batteries internal resistance increases and the charging current goes down. For some reason, the resistance of one battery increased faster than the other leaving the lower resistance battery only partially charged. At least that's my theory. Anyone experienced this situation?
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Old 08-15-2008, 05:08 PM   #12
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I used this set up for a period and found that overtime, one of the two batteries would not fully charge. Charging rate is determined by two factors - 1. the applied voltage and 2. the internal resistance of the battery. As the batteries charge, the batteries internal resistance increases and the charging current goes down. For some reason, the resistance of one battery increased faster than the other leaving the lower resistance battery only partially charged. At least that's my theory. Anyone experienced this situation?
Hundreds of times, during my 42 years of Airstream work.

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Old 08-15-2008, 07:36 PM   #13
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When you install these 6 volt batteries I assume they are in series and still charged by the 12 converter.

I have heard this suggestion before but have a question. How come a couple of 6 volt 300 AH batteries can out last 2 12 volt 800 hour batteries
HowieE,

Look at this chart: Lifeline Batteries - Marine & RV Deep Cycle Batteries. You will notice that the largest battery Lifeline sells.....the GPL-8DA is rated at 255 amp-hours. When you use a couple of GPL-6CT VDC golf cart batteries in series, you still have 300 amp-hours, but the draw down at 25 amps is 662 minutes compared to the 8D which is 475 minutes. The 6CT's still have a smaller footprint than the single 8D and have a much heavier plate structure.

I've been using mine with a 2000 watt sine wave inverter to run corded power tools on the job and have yet to run them down past 75%....even after using them all day!

BTW, which battery were you referring to that has 800 amp/hours?
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Old 08-15-2008, 08:40 PM   #14
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Some factors to consider...

The 300 AH rated 6 volt Lifeline mentioned above are much taller than standard 'golf cart' types...

The Lifeline 'golf cart' sized 6 volt battery is rated at 220 AH's...

Apples and Oranges above when one 12 volt battery was referred to as '800 amps'...I believe that was confused with 800 Cranking Amps....not Amp Hours...completely different.

We want high Amp Hour ratings in the Deep Cycle batteries we use in AS's...consider the AH rating as the 'size' of your electronic 'fuel tank'...the more AH's you have stored in your battery bank, the longer you can run your stuff, or the longer you can go before needing to recharge.

Being in the Battery Biz for many years, I always carry additional batteries with me if my shore power cord is 'too short' (boondocking) to reach an AC power source...and with a larger battery bank, I still attempt to recharge a small amount EACH day, instead of running the batteries longer and then having to run the Gen longer hours to play 'catch up'...

Solar panels would be a big help to recharge a little bit each day, with some Gen running time added in when needed.

I always advise customers to get the largest battery they can fit/afford in their particular application/installation...with our AS's we usually have size and qty limitations...our 28 footer has the two battery compartments in the front...the PO had two gp24, 10 inch batt's in there...upon inspection, I found that the compartment would hold gp27, 12 inch, deep cycle's, so that's what we use.

I still prefer flooded cell deep cycle batteries for their higher AH ratings, and lower cost of investment savings...and I keep an eye on them to keep any corrosion at bay.

AGM, sealed types are also a good choice, but usually the AH rating is slightly lower for the same sized battery group number, and they are approximately TWICE the cost of flooded cell batteries. I don't really consider the 'non spill' advantage as being that important in our RV type trailers, unless you have a custom installation where you need to lay them on their sides.

You MUST have a newer converter/charger if you intend on using AGM batteries...your older Univolt type unit will overcharge AGM's in short order and ruin them...and dealers won't replace under warranty if the batteries have been overcharged...we can tell! Which is another reason I don't recommend AGM's for our trailers in general usage.

Let me know if you have any other battery questions...
Ray in Northern Calif.
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