You need to convert the AC to DC with one of these.
Full-Wave Bridge Rectifiers for Power Supplies - RadioShack.com
It's quite simple. The + and - terminals connect to the Battery + and -. Then the two terminals marked by the ~ get attached to the dynamo. It doesn't matter which because it is AC.
I used this on my 12v,6W bottle dynamo until the bearings went on it. I have a new dyno on order and found this -- TNC Scooters (Scooter Sales and Service)
-- to use with it. It regulates for 12V and rectifies the AC to DC in one unit. However, that unit is for 12V. I think the S/A hub is 6V, 3W.