2001 Boxster. I have checked the voltage on the battery before and after start. The voltage actually goes DOWN when revving the engine.

Has anyone else heard of a problem like this? Does anyone know what the failure rate of alternators is?

 

WHAT IS THE VOLTAGE WITH THE VEHCILE RUNNING

 

12.6 when the car is running.

 

Make sure the battery is full charged as i have seen dead batterys look like bad alternators
but chances are your alternator is bad
they do fail on occasion

 

The voltage should not go down. If the battery is bad the alternator will be trying to charge at about 14 plus volts. Easy to pull the batter and have it checked. Alternator not so easy but doable. Even pulled take it in and have it checked as well. Make sure all cables are good, clean and secure first.