I had a similar issue on my 06 450 exc. It had a ballistic battery, and after using the easy button i found it dyeing out. I even bought another battery thinking it was bad. What I found was after riding and the bike got hot either the regulator or rectifier was crapping the bed. Run the bike around pull the seat and check the charging voltage at the battery. You should see 13-14 volts. when revved up. i was seeing 10-11 volts. it was enough to keep the bike running. I put in a Trail-tech DC convertor system and haven't looked back since.