Most likely the rectifier. I had a similar issue and had to replace the unit with a Harley Davidson unit. The motorcycle shop reckoned existing units were bit fragile. The HD unit more robust. Rectifier is the finned unit bottom right front of engine.
The mount was also upgraded to the three point, from two point. This two point mount is known to fail.
Luckily mine was still in the garage when battery went flat. I charged battery and drove to mechanic to get it checked out.
HD sites have easy methods to check to see if its the alternator or rectifier.
