Did you test the voltage of the battery in two conditions:
1)Car is off, you should read about 12.5V
2)Car is on, you should read about 14.5V

The only generator of electricity is the alternator and it tied directly to RPM IF THE REGULATOR CIRCUIT IS DEAD.

If the regulator circuit is fine you would see very slight voltage changes when RPM is vary and the voltage would be 14.5 ish at idle.

It sounds like your regulator (Rectifies and straightens the DC voltage) is going bad.

Run the tests and let us know.