(above) Batteries: Yeah before this thread I had commented on the seatpost batteries on the Dahon E20; If replacements not available, I think one could package a more cubey battery behind the seat tube, sitting on the chainstays. Assembling an aftermarket battery array is not hard, but I don't know what other components are part of the battery pack in terms of power management, fault detection on individual cells, etc. With lithium batteries and dangers, that stuff is not trivial. 20+ years ago, the danger was enough that the professional, safety-critical project I was a part of, chose nickel-metal-hydride as an upgrade from the previous lead-acid-gell-cell, not making the leap to lithium though that was already available.