There are so many things that can affect when a battery will die, just telling them to get a certain kind of battery is not the answer. Be sure to use the battery as per directed by the manufacturer. Keep the battery clean as even small amounts of dust ont he battery can cause a surface discharge that will drain a battery very quickly (ironically, it is easy to test for this condition).. also every car has a certain amount of parasitic drain on the battery just for the memory of the ecm and other components (lots of aftermarket components such as alarms or head units add to this original amount) of the car, some can be quite high, unfortunately, Ford has a reputation of being the company with the most parasitic drain. You can do some simply at home tests that will help you determine what actually happened, I would guess that after two weeks the parasitic drain just got to the car, but you may want to check and see if you have too much of it.