You are preaching to the choir on manufacturers blaming repair shops for "not knowing how to test" their defective junk. I have 3 methods I use for testing batteries and use all three before taking a battery back to NAPA. They know when a battery comes back from me, it is verified dead. That's part of the trust and relationship. First, I unhook or remove the battery. Then fully charge the battery with an automatic charger that has a deep recovery mode until the charger indicates a full charge. I let the battery sit 24 hours. I check the voltage. If it is 12.4 volts or lower, no further testing needed, it's done. If 12.5V or higher I then move to my capacitance tester. That's the digital tester where you program in the CCA of the battery, hit the go button and it gives you the calculated CCA available. Midtronics is the main vendor of these, but mine is a Snap-on. If it's under 75% of the rated CCA's, again it's done. Third, I still have a VAT 40 carbon pile tester that puts the heavy continuous load on the battery. If the battery can't deliver half of the rated CCA's for 15 seconds and maintain 9.6V or higher, it is done. Failure of any of these tests and the battery will give you trouble in some situation in the near future. Not saying it won't limp along for a while, but will eventually leave you walking.
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