Thanks to the awesome (both technically as well from an entertainment perspective) instructions by Frank Gruendel how to rebuild an Apple Newton batterypack, I managed to revive one of my old, flat packs. It took a while, and was at certain points quite frustrating, but definitely worth the effort. Frank is certainly right about the manufacturing tolerances, even with greatest care it seems that I managed to expand the pack in one or the other dimension to the point that the built in mechanism is not strong enough to push out the pack by itself. Thankfully, Frank has that problem also covered, and I can now enjoy 2500mAh of power :)