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
Thats true Deacon, remembering to keep it charged gets harder to do at my age LOL! Anyways I have 2 batteries so that at least one is always charged and ready to go.
But then I would need to carry them both in case I was out and found the battery dead, then of course one day for sure they both would be dead lol. My memory really does stink.
Of course I could get a dozen batteries and charge them, just in case. I do have a nice trailer I built.