Ford Repair: Alternator, ford taurus, sam s club

Question
Hello Mr Francis! I have a Ford Taurus GL1995 car. The alternator charges the battery when the engine is on while the car is parked. It does not charge the battery at higher rpm possibly. I am told by SAM's club guys that there is some problem with the alternator. I wish to understand what the problem with the car is and how I could go about getting it repaired and approximate cost involved. I'd appreciate your answer very much. I am a novice in this matters and wanted an expert advise before I take it to a mechanic.  

Answer
you can get a rebuilt alternator for around 75 bucks.  Its easy to charge.  Ive never heard of alternators that only charge the battery at idle.  However, if that is the problem, i would guess its the voltage regulator thats the problem and not the alternator.  Dont listen to people who work at sams club.