"?I stuffed 2 Li-ion flat cells into the enclosure and have been enjoying its lighter weight and higher capacity"
How did you rig a charger for those?? I've looked at a couple of options: bring out 3 contacts for a hobby charger, integrate a USB charge module, use the two output contacts and rely on the cell protection or a balance board, or not seal the case and charge each individually with a hobby charger (since re-sealing the pack is a bear).
I'll probably just buy another factory pack when mine fails, though, unless I want a project at that time.
radellaf