Voltage is important. But for thick plate low CCA batteries a significantly lower amperage draw must be used coupled with a significantly longer test draw time.
I have found too many bad batteries that fell on their face after 20-25 seconds.
As a general rule with thick plate batteries applied amperage will cause an "X" voltage reading. The voltage will remain very close to the initial value throughout the test. If it degrades more than .2 - .3 volt toward the end, equalize, condition and re-test. A repeat voltage slump means a battery is on it's way to the recycler.
