Because I'm gonna miss my mophie like crazy once my 5 shows up on Friday. I use my phone ALOT for work almost 2 full charges a day on my 4S so it's convenient to have the mophie and still only have to plug in at night. This morning at 7am full charge I ran it down to 18% by 4pm mophie charged it back up to 100% and I'm down to like 40% now before I goto bed. Need a battery case! Hopefully mophie designs these things pretty quickly.