96 buick lesabre losing voltage

I have a 96 buick lesabre custom edition, and in the past month I have noticed that the volt gauge in the dashboard has been fluxuating. If I have the heat on and come to a stop at a stop light the volts in the car will drop from about 17 to 13, the lights will dim, and the amount of heat coming out of the car will diminish. I replaced the battery and the alternator, and the problem still remains. I have no idea what else it could be and afraid that the car will stall during winter while Im snowboarding. Any suggestions to what the problem may be will be a great help. Thanks

my car does the same thing, its worse with the rear defogger turned on. its normal I guess, the alternator doesnt make enough power to compensate for the large load on the battery at idle. might think about getting a higher output alternator, should cure it

How easy was it for you to find a more powerful alternator, and how much did it cost you? Did it completly solve the problem. Also did you car ever stall while this was going on? Thanks for your help it is greatly appreciated.

yeah, no problem. My car never did stall when this occured, seeing as it was still within the normal voltage (12-16 ish). The factory alternator simply does not make enough power at idle, with the high load created by the heater, lights and defogger. It is fine to drive it like that. I havent changed the alternator in my car, but you can probably find a good one through napa, autozone etc. They sell them a lot for car stereo applications.