They could very easily be pedal powered, requiring no charging or battery changes ever. Old dynamos resisted pedaling because of the old lamp technology, and the lamps also burned out often. No more. This seems to be a nice diagram, a rectifier and a couple of capacitors to make it DC for the power led, might try doing something like that one day and putting the power led inside my original Peugeot PX-8 luxury tourer’s lamp, straight from 1975 and still going strong.
The PX8 at the Lepsämäjoki river valley in hot and smoky August 2010.