HI Marty,
Thanks for posting about this!? I used the original case and flat Li-Po cells and enjoy longer battery life and less mass.? See post "HB battery pack using Li-po cells".? Your solution using removable cells has a big advantage because you don't need to modify the battery's charger or make another one.? Just take the cells out, put them in the charger, and put charged ones in.? If you're on a long outing, you just bring along a couple extra freshly-charged cells.
Cheers,
Halden VE7UTS