I run an SP dynamo with a Forumslader setup. My light is a cygolite expelion rechargeable that is okay at best as a headlight which is fine because I don't ride at night often, but doubles nicely as a camp light. I keep my phone plugged in and charging while riding, use the cygolite as a very occasional headlight and as a camp light in the evening then plug into the battery pack to charge overnight then repeat the following day. I average between 13 and 17 MPH with my long distance average being a solid 15 MPH and find at 15 MPH I can bring my iphone from 70% and Forumslader from ~85% to a full charge in around 2 hours of riding, that's with the forumslader app running and screen on 100%. As an aside I also have a Sinewave Revolution and though I like it for being waterproof, have to say it's not nearly as efficient or nice as the Forumslader with Bluetooth. If you are planning on purchasing a USB charging outfit to go with it give the Forumslader a long hard look as it really is worth the extra $$ over a Sinewave or similarly priced USB charger. Having ridden a couple of seasons now with a Dynamo Hub I have to say I wouldn't own a touring/distance bike without one but do plan on building up a traditional hub wheel over the winter so I can swap between dynamo and non dynamo during my 30 mile commutes to see how much my average speed decreases when I use the dynamo.