I've found several reports on people with bad internal charging circuits for Dell Latitude PCs (I currently have a Latitude C600).
The symptoms include:
-Battery does not charge
-High pitched noise coming from motherboard when plugged into AC adapter. (this is not fan noise - most likely FET?)
I cannot seem to find any information on how to fix (mine is out of warranty). This sounds like a pretty common problem so I was hoping that someone here had some additional information on how to fix. This is not a battery problem as both charge fine in other laptops. Please respond to junkbox1001 (at) yahoo (dot) com