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Old 11-11-2012, 02:57 PM   #21
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OK, so here's the spec on the Interstate SRM-29 (group 29) RV/Marine batt.

RV Deep-Cycle/Starting Batteries

210 RC and 675 CCA (How is RC calculated?)

93 aH by 15Amp method
106 aH by 5 Amp method (right????)

Here was the answer from Midtronics: (name withheld pending permission from author of the email to disclose)

"Hello Rich,
I'm afraid not. Years ago, a VERY generic rule of thumb was multiply aH x 3. However, that's not going to be reliable. There is simply too much variation in battery designs. We get this question a lot, and here is my answer that I keep on file:

Ideally, you need a cranking value to test against. If the battery does not have one listed, then first contact the battery supplier or manufacturer to request a CCA, CA, or MCA value -or any other value that your tester has available (CCA is recommended). The next best thing would be if you have access to new batteries of the exact same kind (same manufacturer, everything same). You would take readings on a sample of say 10 new and fully-charged batteries, add it up and divide by 10 to get an average and use that as your test number going forward. You may need to tweak it up or down as you gain experience, but that’s a good starting point. Now that you have a CCA or other valid cranking value to use, let’s make sure that we’re clear on what the test results mean. Testing a deep-cycle battery against a known cranking value provides useful information, but is not a definitive test. I have an analogy: Think of a cranking battery as a sprinter, and a deep-cycle battery as a long-distance runner. A deep-cycle battery that meets its’ cranking performance may not meet its’ deep-cycling capacity (it may run the sprint but not the marathon). A battery that passes an established cranking value ensures two things: 1. The battery meets its’ cranking rating, and 2. The battery has no gross failures such as a bad-cell or short. Both are positive indicators, but, again, not a guarantee that the battery will meet its’ deep-cycle rating. Still, a good CCA test with one of our testers is better than the alternative of a timed-discharge test –and it’s certainly better than guessing or just going by voltage and time-in-service, etc. I hope that this information helps!So multiplying be 3 isn't too accurate (that would equal 630 in my case vs. 675 per Interstate."

The one thing I can't really figure out.. I couldn't make my batts fail until I erroneously input 1300CCA I know by batteries are healthy, but double the spec??????
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Old 11-11-2012, 03:19 PM   #22
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Found it:
RC (Researve Capacity)

BCI defines it as "the number of minutes a new, fully-charged battery at 80F (27C) can be discharged at 25 amps and maintain a voltage equal to or higher than 1.75 volts per cell" (i.e., 10.5 volts for a 12-volt battery). This rating represents the time the battery will continue to operate essential accessories in the event of a charging system failure.
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Old 11-12-2012, 11:50 AM   #23
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Hi dzn.

There are a number of true deep cycle Group 27 batteries that also bear a CCA rating, which is usually in the vicinity of 600 CCA. I would use that as a starting point as you test batteries. The Interstate Marine battery you mention lacks an amp-hour rating and is better understood as mainly a starting battery.

I don't have any inside knowledge on how the Midtronics tester works, but I would imagine that won't "fail" batteries until they only deliver around half their rated CCA. The CCA rating is a "when new" rating and deteriorates slowly over time. Batteries that have really failed usually won't deliver more than 20-25% of their original CCA in my experience, and often less than that.

In other words, the setting doesn't matter that much -- there are few marginal batteries out there that will pass at, say, 400 CCA while failing at 800 CCA.
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Old 11-12-2012, 11:56 AM   #24
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I suppose if I really want to know, I should run my batts down to 50% and maybe 75% while in the AS. The Trimetric monitor will measure the aH used since last charge and its corresponding voltage. I was looking for a way for this tool to give me a "health" status because it is a quick 15 second test.

I do know that these batteries, when new, delivered 190aH (combined) when discharged to a 50% level. (12.2V if I remember the spec correctly)
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Old 11-12-2012, 03:04 PM   #25
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I expect that if your batteries put out a good CCA number that they would be in pretty good shape. I expect that a battery that has a low CCA would not put out its rated AH's. I also expect that a deep cycle battery would not have the same CCA as a car battery. I would think that if you test a new deep cycle battery and a new car battery you would have at least a qualitative comparison.

If car battery puts out 1000CCA and a similar sized deep cycle puts out 500 CCA. Then you know if your fully charged deep cycle only puts out 200CCA that it is probably on the way out and will run down long before it reaches the rated AH.

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