I'm not building cells yet, but got a question on this for ya.
If I see that correctly, are you soldering a strip all the way across the back of the cells AND running the back of the plywood also? If the cells are wired end to end how about 2 small holes at each joint, one for each cell and solder them there. Sort of stitching them in. Each only needs enough tail to loop over the hole to the next tail, the plywood doesn't need any on the back side for anything and any holding strength is just right at the holes anyway.
Doesn't sound right the way I typed it, I know what I mean, hope you do too. Anyway seems like it would use about half as much ribon if it works that way.
Also not sure how your laying out the holes, maybe one of my tricks will help you on that. When I needed alot of holes exactly spaced in several sheets of wood, like building shelving, I first cut the panels to the size I want them. Then cut a sheet of Peg Board to the same size. Clamp every thing together with peg board on top, count the holes and drill!!
Every sheet comes out exactly the same without having to measure each one and worry about any errors. Saves time not having to measure anything or just a top sheet. And of course the biggest time saving is drilling 1 hole and getting 4 sheets done, cuts the time to far less than 1/4 of doing each seperatly.
I do that alot when building stuff like 1' deep X 6'wide X 8' tall cases/shelves to store DVD's 8tracks, VHS, Cassettes, etc.. Every thing is a different size so I drill all the up rights for ajustable shelfs. Drill, count 3, drill, count 3
Most the times I don't care if the holes go to the outside of the unit, if I do care on one I just drill the two end sides seperatly using a little electrical tape on the bit as a stop guide for the depth. Still use the same pegboard piece as a guide though and all the holes come out correct.
I pretty much do the same thing for measuring cuts and other stuff too. Clamp everything together find the center hole and use a pencil to fill them in. Take off the pegboard and connect the dots, normally a pefect straight line better than measuring and using a square etc.. Provided of course you can cut that thick, or do each seperatly and they all still come out the same.