Ok, I think I get it. 3 out of 5 batts are acting up. Your ends are wired correctly too.

I can't duplicate the problem , but can only guess it is the female connector being worn out. A quick test may be to plug the terminal in upside down to test the fit/continuity/wear of the neg and then plug it in "off-set" to test the fit/continuity/wear of the + one. I know it does apply the spring part against the mating terminal, but still may give a clue to where the trouble is.

Another idea is to check continuity of each pole to see which is giving trouble + or -. I'm guessing they wear about the same, yet the - is the culprit considering the presure you put on it sideways. What is surprising though is that a side pressure either way will break connection.