I was thinking more along the line of a battery that you charge as you ride to cover slow moments.
If you use this all you would have to add is a way to limit charge to Capacity/5 (if you knew the alternator output) and a current limit resistor to the LEDs (if you knew what they were). It will shut off when fully charged and discharged. Look at the schematic on page 9 of the data sheet. This is to keep it from catching fire
MIKROE-1120 MikroElektronika | Mouser