Is it possible these things have been sitting around for some time between manufacture and use? Lead acid batteries can become a little twitchy if they're not used for a long time, and may take several cycles to 'wake up' to the point you can draw useful current from them. A really bad one won't produce any current at all, even though the voltage can be spot on, as the internal resistance rises too far.

This is also the normal method of death at end-of-life for lead acid cells. But that normally takes either a few years use or a few years disuse. A few years, anyway

pca