It has built in plugs so you never need to carry a cord and/or a charger
The battery detaches from the protective inner case so you can recharge your battery while your phone stays with you, protected.
Here are some other features of the PWR Case and a video explaining the product:
3500 MaH Battery gives you 130% more battery to your iPhone 6/6s
MicroUSB port allows for cabled charging in a car or at your desk
Protective inner case so your iPhone is protected when you don’t need the extra battery or are recharging it
Packaging includes and Audio adapter for your headphones and a MicroUSB cable