PowerBoost X1 2600mAh Premium Portable iPhone Charger Rechargeable Battery With USB To 8-pin Connector Cable (Works with iPhones 5 / 5s / 6) And With USB To Micro USB Cable (Works With Most Android Phones) from Duroplus
It works for my LG G3 smart phone, but it doesn't charge very fast and it does last very long.  I've used it while traveling but it seems like it dies after only charging for an hour.  Helps me in a pinch, but doesn't charge/last like I expected it would.