The Motor Industry Research Association spent a lot of money testing, building and destroying many electric bikes.
Their conclusions were:-
1/ Battery packs, either NiMh or Li-Ion do not have the capacity to be viable for distances over 40 miles.
2/ Riders get laughed at by pedal cyclists. - This was from the bitter experience of MIRA engineers, and this simple reason would deter people purchasing an electric bike.
3/ The cost of replacing the battery pack on an annual basis, Li-Ion in particular, was far greater than the maintenance cost of a conventional bicycle.
As a cyclist, and working at MIRA, I was asked if I would 'test' the bikes to commute 17 miles each way. I declined, and the response was "I'm not surprised, we can't find anyone who will ride the things".
The only electric bike I would consider riding is a Yamaha Derney I saw in a magazine once, but I can't find it on the internet. Maybe the project was scrapped.