The Duo (or any of the Hyperions) used to come with only the Hyperion style balance adapter board. There are 3 other types of balance plugs in popular use so you need one of the other adapter boards. The other types are the JST-XH (also called the Align style), Thunderpower type, and the Kokam type conmnector. There are two that could be called 'small' connectors. Look at the listings here and see if your lipo is listed - it'll tell you which adapter board you need to buy -

http://www.allerc.com/product_info.p...oducts_id=3160


What brand is your lipo?