Consider the advanced technology of rechargable batteries. There are some flashlights now that use Li-Po or Li-Ion batteries that should be super bright and long lasting, with enough power to run a healight/tail light for hours.
On my Briggs & Stratton, Clinton, Jiang Dong, and Lauson, I use the rubber support wheel off a clothes dryer to run a bike tire generator. I can retract per usual when not needed. Keith (trackfodder) Williams