I think ~1996 is when the appropriate batteries were generally available. Before that, the existing battery tech wouldn't have fit inside a frame. Around the same time, when my friends and I were working at Moli Energy, we would scrounge for rejected cells and stuff them into water bottles. Coupled with a DC-DC converter, they were perfect for running insanely bright halogen lights for night riding. Charging was dead simple too. Just connect to a constant voltage source (i.e., the variable power supplies in our lab) and limit the current to an amp. Let sit for a few hours and away you go.sniper said:John, great post. But please specify 'hidden motors'.
Varjas has shown how to fit an old model crank assist motor nicely into a 1998 Trek bike.
And we have the first crank assist bike on youtube from 1979.
The only problem there was the big visible battery pack.
But the battery problem for crank assist would have been solved by the late 80s/early 90s already. Not 2007.