Amazon offers OtterBox Wireless Power Bank for MagSafe, 3k mAh - Black for free shipping with Amazon Prime.

Product Description:
Wireless Power Bank for MagSafe keeps iPhone charged. Simply click onto iPhone or OtterBox case for MagSafe to get a boost of extra battery power on the spot. Or use as a standalone power bank to charge other devices. Power Bank for MagSafe delivers all the power you need to stream, work and connect.