Volvo Repair: abnormal charging, ac delco, volvo s60

Question
Hi Roger,
  1998 S40 2.0T. I have a voltage recorder hooked to cigarette lighter socket. After the engine starts, I notice the voltage begins with around 14V. As I drive for 15~20KM, the voltage starts to drop and then goes down to 13.0V after 20-minute drive. To fix it, I've just replaced the battery with Hoppecke 56518(70AH) and changed the generator from Volvo 80A to ACDelco 120A. After money spent,this phenomenon is still there. My technician ever additionally wired the GND between the generator and battery. It didn't improve it, either. An interesting thing is that the battery was full when I took it off , trying to charge it with a separated charger. I am wondering whether the generator's charging voltage will naturally drop after a battery is charged full. I'm prone to believe that there is something wrong when the engine trunk gets hot. Could you kindly advise? Thanks. By the way, the same voltage recorder is used to record the voltage of my another Volvo,S60. The charging voltage is always shown at around 14V, which is just to exclude the possibility that I have a bad voltage recorder.

Answer
Brett, well anything AC delco is nothing but junk so that is the first thing to get rid of and find a nice bosch unit.  Normal charge should be between 13.5 and 14.0 volts, you arent in that bad of shape.  Does the car die on you or leave you stranded?  Roger