What can cause battery drain on a F350?

Just setting for a week can run the battery down. you need to make sure that your grounds are good, that your alternator is charging at the proper rate and that the voltage regulator is working properly. If all of this is good then you can start unplugging things that drain the battery, radio, power door locks, interior lights etc.. Or if you know how to use a multimeter you take measurements to try to figure out what is draining the battery. Just be aware that a bad ground and all of the stuff that is contantly on (clock, radio memory, ECU memeory...) will drain the battery some. the process of driving the auto daily maintians the battery charge. The newer the vehicle the more power they usually draw an a daily basis. With out further info it is impossible to know what is going on.