This is my trusty BikeE. I've had it about five years, and it's still going strong. I had to add the electric power assist since my accident in October left me with a weak right leg, and a limp. It's powered by lithium ion polymer batteries, just like your laptop, so it's not too heavy. This gets me to work and everywhere else I have to go. If you'd like more information about this system here is a link to it's creators.
http://www.ecospeed.net/index.html