I have a Mophie Juice Pack Plus, is it better to run the phone battery down first or run on the Juice Pack first.

I have a Mophie Juice Pack Plus for my IPhone 4S. Is is better to run the Mophie down keeping the phone charge up or run the phone charge down first then recharge with the Mophie. Does the phone battery get weaker after so many charge cycles like the Mophie and other external chargers and boosters.

I am able to keep a 100% charge on the phone battery at all times, I have 2 Mophie's I swap them out when they run out keeping my Iphone fully charged at all times. Will this hurt the internal phone battery?

Bob Daig