Oh vey
"Cook, who was in New York attending an Hour of Code session on Wednesday, told
Mashable that other battery cases like those offered by Mophie
">are difficult to put on and take off due to their rigid full-length battery packs.
"You know, I probably wouldn't call it 'the hump,'" Cook said, referring to the protruding battery pack. "If you make this solid all the way across, in order to get it on, you'd find it very difficult to get it on and off. So the guys had this great insight to put the bend in along with making it a smart case."
http://appleinsider.com/articles/15/12/09/tim-cook-lauds-new-iphone-6s-smart-battery-case-design-as-easy-to-use