I had 2 hump pacs go bad at the same time - took both apart and found there were 3 bad cells - rebuilt a 5 cell hump pac using good cells - works fine. Mine were hpi - cells were glued together with what looked like hot glue and came right off. The connection between cells were those spot welded pieces of thin metal - pulled those off with needle nose pliers. Smoothed off the rough spots on cells and used 14ga wire between cells. I glued cells together with a dab of shoe goo. Works great, still working.

Only suggestion - use something to cover cells ends so you don't get a short. Mine had thin cardboard that wa sadhesive on one side - I just re-used that.