Electrical problem
1994 Jaguar XJ6 6 cyl Front Wheel Drive Automatic 106000 miles

I cannot keep a battery running in the car. I can drive the car for numerous days straight in a row with no problem and the next day the car is totally dead. I have brought the car to 2 different mechanics numerous times and they can not find the problem. When the car is off, nothing is draining on the battery. Is this a common problem with the car? Someone mentioned perhaps its the dioid?