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)
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??????