"3) Facing the fact that there are connections between the various cells in the stack the optos across each cell will be directly affected by the current paths from higher cells and those below that feed to the GND rail. This would disrupt any accuracy of reading any one cell."

If the current percolates down, then the current through each cell-load will be equal to current through the load because of cell + the current from upper limbs. In this case, the drop across the cell-load will be more than the cell voltage ?

"Last comment I'll make is that you say that you want to not have to be concerned about the order of the cells and their location in the stack. If that is the case then why are you monitoring?? I thought the point of monitoring was to be able to isolate the cell that may have a problem. "

I actually need to identify the cell, but input connections would a lot easier if I can opto it. I only have to tell them which opto connection is suspect.

As you said, I shouldn't be using Optos I think, even though it is too tempting. Everytime I used optos I had calibration issues.