I Run the lights wired directly off my hub dynamo, Edelux, now, E6 last few winters..[+ taillight]

6v3w to usb converters , it seems, are to run the many electro widgets,
people tour with.. i didn't.
had some solar chargers,
but they need to be in 1 sunny place, not on the move.

cubicle bound commuters recharge their USB light batteries at work,
for the trip back.

Staying in a Hostel/B&B, occasionally, gives you mains access.. on tour.

but as the high latitudes in the northern summer,
leave you with lots of daylight cycling hours to make camp,
a small battery light may be sufficient.

I have one in my Folding bikes front bag , just rechargeable AA,
It is not my commuter thru the winter, now.

best to have a few backup light options, a 2-fish right angle 2 strap,
holds a common compact flashlight on the handlebars.