Step 1. Take it to an auto electrician.
Step 2. Pay the bill.
Problem solved.
Might be the voltage regulator, not regulating the voltage.
If you have a multi meter, check the voltage at the battery with the engine running at idle. then get someone to rev it to 3000 and check it again.
I dont know what the voltage should be, id be guessing if i said, so i'll leave it up to someone that knows, but there shouldn't be much of a difference between the two speeds. If its any more than 15 volts, i'd be worried.
If you have the original VR, I belive they can be serviced, but you'd have to do it yourself, VR's these days are electronic, and an auto electrician would replace it with the electronic type.