With what you discribe, It sounds to me like your battery maybe going south. Here's what I would do... Remove the battery, clean both ends of both cables, look to see if you have corrosion building where the terminal meets the cable conductor. Take the battery to either your favorite bike shop or a auto parts store and have it load tested. That's really the only way to properly check a battery, and see what results you get. That should give you a good idea of what you are dealing with. If all the above check good, then you'll have to check the charging system... See the self help section and or re-post... Good Luck.