I have a 2001 Sephia that, I think, has a bad alternator. With a new fully charged battery I read a normal 12.5 volts. After I start the car the voltage increases to 13.7. Again, normal. If I increase the engine speed to between 1500 and 2000 RPM the voltage at the battery terminals drops back to 12.5. Not normal. If you drive the car long enough the battery will eventually be discharged.
I took it to the dealer and they said there is nothing wrong with it.
As far as I'm concerned I thing the alternator is toast. Am I on the right track or am I way off base?
Thanks,
Mike