That's only going to work if you have a dynamo that delivers a regulated 5V DC. The USB rechargeable tail lights have a 3.7V lithium polymer battery inside and the electronics to allow it to recharge with 5V DC. When you plug it into a USB charging unit it gets the right voltage for the electronics inside the flasher to recharge the battery. Instead you could wire up a 3.7V Li-ion battery like the 18650 batteries in parallel with the battery inside the flasher. That would give you a much longer run time than the internal battery. I was going to do that with an inexpensive 100 lumen COB taillight but wasn't able to open the light without damaging the case. When the internal battery begins to die, I will sacrifice the light and see if I can use an external 18650 battery. Even the cheap taillights warn you to not go over 5V DC on the charging circuit.