1992 Cadillac Deville Cadillac problems

Electrical problem
1992 Cadillac Deville 6 cyl Automatic 100 miles

the car is a 1992 cadillac deville the battery keeps going dead when you drive the car it works fine
but when you bring the car home and don't drive it
for a few days the battery goes dead and you have
to charge the battery then the car works fine again
until you bring the car home and don't drive for a
few days the battery goes dead again but the car
works fine if I drive it everyday but when I bring the
car home and don't drive it for a few days the
battery goes dead again I have changed the
old battery with a new battery and the car works
fine but when I bring the car home and don't drive it for few days the battery goes dead again
the car is computerrised the mechanic says the car
has a short in the car but doesn't know where
the short in the car is at
wan't to know if you can help me out

THANK YOU