Apple has a $99 Smart Battery Case
Smart Battery Case, a $99 (£79) add-on for the iPhone 6 and 6s that packs an extra 1,877mAh battery into a... curious-looking silicone frame.
Extends the battery life on your iPhone 6/6s
Acoustic port makes audio sound better
Comfortable to hold onto
Expensive compared to the competition
No on/off switch for the batterY