One thing I wonder about the yesterday's double-battery system.
I connected the blue cable to (-) pole of the battery 1 after the circuit board and not before it, like with battery 2.

Now, if there is a shortcut in the 2nd battery, the protective circuity of the 1st battery is disabled and it shortcuts also battery 1.

I didn't find a place where the cable could be attached so the circuity would be in middle of it and the battery itself. How about with those other batteries you have tested?
I reread (Nth time) your first post and looked the pictures, but I am not sure how you have the 2nd battery connected. At least the 1st battery you seem to have connected same way as I have now, skipping over the battery's own (safety) circuity board directly to the poles of the battery1.

I regret I didn't take more macro photos of the Nokia BL-5J battery when I had it open. I have a good photo from front, but should have taken one from the side also to show where the cables really are connected.