I have a Shimano 3n-72 dynamo hub and I have a LightCharge USB charger so I can charge an external battery pack. When I took off on a recent trip, my battery pack showed three out of five bars of charge. I hooked it up to the charger and rode for approximately 5 hours. The battery indicated that it was charging as I rode (bars lighting sequentially as I rode) but at the end of the 5 hours the battery still only showed three bars. When I got home I connected the battery to a USB port on my computer and the next morning the battery was fully charged.

My question is, from what I have described, does it appear that my battery charging while on my bike ride? Is the output of a dynamo low so that it takes a long time to charge a battery? Anyone have any experience here? I am going on a long bike tour in the next couple weeks and I want to be able to keep the battery charged up. Any advice or thoughts are appreciated.