Check your ac out put from the stator and check it with the specs it maybe over charging the system. make sure that you reg/rec is grounded good
Mark
C.C. Motorsports

Also if batt is old n worn..may b drawin tumych juice from chargn parts. It shud always read 12.6v

There is also a device called a regulator,, this regulates the amount of current passing through the system..

As you speed up the alternator pushes more power.. the purpose of the regulator is to beak down the excess voltage so the lights and batteries and stuff get the required voltage..

replace your regulator and check for burnt wiring..