I own a 2006 Taurus SE, with about 75,000 miles. Initially I brought the car into the mechanic because the Check Charging System warning and Battery Light came on. The mechanic said the serpentine belt and battery needed to be replace. He replaced them, and said the alternator appeared to be working fine (running at 13.8V). After driving home from work later that same evening the Check Charging System and Battery Light came on again. I brought it back in and now the mechanic is testing the alternator when the car is fully warmed up to see if it is charging the battery (increase in voltage/decrease of voltage in the battery). If the voltage decreases in the battery the alternator is probably the case. If the voltage increases in the battery (alternator checks out fine) what could else be the problem producing the Check Charging System warning and Battery Light to come on? Is it the computer in the car?