If you wanted to convert a standard 29" mountain bike to an e-bike, what sort of motor would be required? Typically they use 48vdc motors, I think, but is that a necessity? I was just interested im something really basic, for emergencies, 3-5 mile capability. Speed isn't too important,~10mph would be nice.
And how many 12v standard (lead acid?) batteries would be required. And I don't mean motorcycle/marine battteries, but the ones you find at walmart in sporting goods.

The kits seem unnecessarily expensive. Of course, unless it's necessary. Ignore all the mechanical aspects. I'm mainly interested in what to look for in a motor, and accompanying batteries. I wouldn't be adverse to buying a lipo battery, but would rather avoid it.