I did this write-up a few days ago that may be on interest.

http://www.bikeforums.net/electronic...evolution.html

I tested two different battery packs with my dynamo. One would not accept a charge at all. As mentioned above, the best way is to answer your questions is to measure the actual output. You can buy USB "power meters" to do this, but the easiest way, if you have some basic electrical skills would be to measure with a multimeter.

What's the capacity of the battery pack? (mAh) Keep in mind that if it's a large pack, it may take a long time to charge with a dynamo.