if you have a manual it will tell you how to check the rectifier and the stator etc. Barring a major component failure always check the connections and put dielectric grease on all you couplers at their connections. Another very important place to check is the ground. take it off the frame (one bolt) and wirebrush the connection site and then put it back and see if the problem is fixed. If the starter is going bad or has dirty brushes it will draw too many amps when starting and make it seem like yopur barrery is low or bad also. good luck.