Today's USB-rechargeable, lithium ion battery technology is a far cry from batteries of a decade ago. The ubiquity of the USB charging standard, decreasing battery cost and substantial research in battery technology only means this solution will get better and cheaper with time. Four-day pedaling power-according to our calculation here- in the palm one's hand is hard to ignore while dynamo hubs designs are near their maximum output, and it is hard to see how they will keep up with battery technology. Economies of scale favor battery technology. Another factor in favor of batteries is that they are platform indifferent while a dynamo hub is specific to a particular wheel. I bought a fancy dyno hub for my 406 wheel. Great, how do I use it on my 29er? We may well be past peak-DynamoHub.