Bob- I enjoy the pictures. What am I looking at in post #1?

Did you take a hack saw and cut open one module to look inside?
Is the case just plastic?

In the Fords, we have 250 "D" cells. I am hoping if I ever find a defect, I can just swap out one ( or a few ) of the "D" cells.

But how would one, or a handful of new D cells behave with over 200 "old" cells? But I also suppose if I go to a junk-yard, I could find "aged cells" so they would be similar performance substitutes.

I read you had trouble with your drill holes not sealing.
May I suggest keeping the holes as small as possible ( 1mm ) and using a syringe to add electrolyte? Then maybe you would have more success sealing the hole. Maybe you could use a hot wire, or soldering iron to "melt" the tiny 1mm hole closed again?

-John