We looked into the available options for most of the last year. I signed on for the Yahoo newsgroup power-assist, found the forums at Endless-Sphere

As we looked into it, there are all kinds of good motors available and a number of ways to hook them up, from front and rear hub (brushed and brushless, geared and direct drive) motors to the Stoke Monkey to a number of other unique approaches. They all work well for particular uses. Industry use of electic motors is immense and that technology is highly developed.

So choice of motor or drive system is not the rub. The rub is batteries.

Sealed Lead Acid batteries are reliable, reasonably priced, widely available, and heavy. Lead is, well, heavy as lead: a mid-sized automotive battery weighs around 45 lbs! The NiMH (Nickel Metal Hydride) batteries are lighter but much more costly and have other problems. Lithium Ion seems to have a lot of potential because of their high energy density, no memory effect, and no real internal discharge. Lithium Polymer batteries are also getting closer to market. But they aren't practical now. And wait till all those smug "environmentalists" who bought a Prius have to replace their batteries and dispose of the old ones and that won't seem like such a great choice.

Going from SLA to NiMH batteries would have doubled the cost of the kit. But this will change. If batteries become more practical, more plug-in options become available (many Northern cities have plug-ins on parking meters for block heaters in cold weather, so it's possible), and perhaps gasoline continues to increase in cost, ebikes may well replace small scooters and mopeds as the most popular short haul and urban personal transportation. Right now, it's tough to beat a 50cc gas engine in the marketplace even though they're stinky and noisy.