After hearing about battery pack failures for the last ten years, I decided it was time to actually see what goes wrong with the subpacks, and see if there is a way to restore some of them. Ron from Hybrid Battery repair gave me a couple of dozen subpacks that had failed for various reasons, so that gives me some examples of the failure modes.
I made some rugged hard copper spring clips from a piece of 1.5" copper tubing. The tube was cut in half, then reformed over a 1" steel rod in a vice. This worked perfectly. The copper clips had a heavy copper braid soldered to each, so I can charge or discharge with high current at the cell level, or zap the cells individually with a capacitor discharge.
First subpack was totally discharged by shorting each cell until they were totally depleted. This is safe when it is done on a cell by cell basis, as the cells cannot reverse.
I put the subpack on a 350ma charge and I will let it charge until it reaches a stable max voltage.
Then a high current discharge while watching the voltages. I hope to finally determine the possible failure modes and see if anything can be done to fix them?