I have little idea on how a battery charger works but i'll just state here what I think is the case and then state my queries. When you receive an AC input from the mains there is first a step down transformer which lowers the voltage - then there is some regulation and it is converted to DC. This current is sent in the opposite direction of a battery which charges it. Now my questions are... 1. Can we use a much smaller AC signal for this purpose - Something like the signal generated with a bicycle dynamo and then step it up\down as required. (what is typically the volatage produced by a bicycle dynamo) 2. What types of batteries can be charged in this manner? Thanks a lot.