I want to get dynamo, too. Only problem for me is that I have too many bikes, and I know that once I have it on one, I'll want it on them all.
Anyway, I am now using a 100 mAh Li-ion battery for keeping my phones (I usually carry two) and my GPS charged. It stores enough juice to keep all gadgets charged for a ride stretching over a complete two day weekend. If I were to do longer rides without any chance to recharge such as 1200 km brevets or multi-day touring totally off the grid then I might reconsider, but for now I am only using the dynamo hub for the lights, which use considerably more power than phones do and therefore are difficult to support with batteries.
Both of my bikes use Shutterprecision dynamo hubs and B&M Lumotec IQ Cyo lights (Premium on the NFE, N Plus on the BF). When I cycle at night I don't worry any more than if I was driving a car. On a 300 km brevet I ride in the dark for about 7 hours while on a 400 km brevet it's basically the whole night.
Likes: leicaman and stu_kawagoe