Jackery Jewel, 2-in-1 Apple MFI Certified Lightning Power Cable with Built-In Emergency Compact External Portable Charger, Cable & Battery Combo for Your iPhone (2016 iF Award Winner)
It's a lightening cable with a small 450mAh battery. This is meant for emergency purposes to give you the extra 10-20% charge in case you are about to run out of juice.
They are offering a 20% launch special (use code JERJEWEL) for $16 shipped.
Looks interesting. Here are some specs from amazon's page:
[Award Winning] Jackery Jewel Cable - Very FIRST Apple MFI Cerfified 2-in-1 Lightning to USB Charging Cable Integrated with Compact Portable Battery for iPhone, Cable & Charger Together Two-in-One Combo.
iF AWARD WINNER Jackery Jewel in the 2016 iPhone category, the prestigious design award validates the unique & elegant very first-of-its-kind design.
MULTI-FUNCTION 2-IN-1 COMBO allows Jackery Jewel to either be plugged into your iPhone mobile devices for up to 20% extra battery power when you're on the go, or to be used as Lightning to USB cable to charge from any USB power outlet.
POWER BOOSTER This portable battery keeps your iPhone 6S #StayCharged for up to 3 extra hours, tiny yet powerful backup companion for iPhone.
JACKERY GUARANTEES the quality of its product with worry-free 18 month product warranty & friendly Team Jackery customer service & tech support. Welcome to #JackeryNation !