[Al Skierkiewicz]

No, likely the connector was dirty or had a spring issue. If you were clamping directly to the terminals on the battery, who knows what was on them. Now that you have a more reliable setup, it would be nice to perform a second test on one of the shorter life batteries to see if it duplicates your earlier tests. Normally, a higher current would have broken through some of the surface dirt.
While we are on the subject, when we put terminals on the battery, I put a star washer between the terminal and the battery terminal. This serves two purposes. One it bites right through any surface crud on either terminal and second it prevents any twisting that might loosen the hardware. Once tight, I believe it to be pretty gas tight and we don't worry about it. We have some larger heatshrink that covers both terminals and the hardware pretty nicely.