This was one quick concept from a set of designs I did in 2014 for a new type of iPhone 6 battery case. 

 

Many existing powerbank / case combos add considerable bulk to the beautifully slim silhouette of the iPhone, making the device clunky and heavy. (Have you ever tried wearing slim-cut jeans with a battery case on your phone? No bueno.) This concept is based on a minimal rubber case with a modular battery attachement that can be added as necessary. Go with the battery pack for long days of heavy phone use – or rock the minimal case on its own for daily service. 

 

The attachment mechanism "rotates" around the apple logo, ensuring that the iPhone (and not the case) remains the star of the design. (Too many cases on the market are full of unnecessary features and try to steal the show – which betrays basically all of Apple's design prinicples.) A hard stop point and rotational attachment mechanism ensure that putting the on / taking it off the battery is natural and intuitive. And the user slides the Apple lightning connector into the iPhone using a familiar interaction (like an on / off switch) to activate the battery / turn it on.

 

This design was done to Apple's design specifications / tolderances. All speaker holes, keepouts, headphone cables, etc. are functional and accounted for in the design. Modeled in Solidworks and rendered in Keyshot.