it will be one of four things,most common is the battery itself needs replacing
2nd is the regulator/rectifier isnt working
3rd is the generators charging coil isnt working properly
4th is the wiring looms has a short to earth somewhere
the best thing to do is take it to a GOOD motorcycle garage and ask for a charging check and a battery load test this will tell you the root of the problem.
adam bike doctor, February 2009
