I had a similar problem with my countax C600, it needs a new 12v battery regulator. Briggs and Stratton do it, available for about £70.00 on e-bay.
kk, June 2009
Thank You Very Much, I Will Try That
John, May 2009
This very simple charging system is controlled and rectified by a single diode, in the red wire going from the engine to the battery. It looks rather like a bullet connector, and its best to fit a new one.