Capable of charging 4 smartphones or tablets on a single charge (two simultaneously) this 15000mAh portable battery pack is only $19 on Amazon today only. The KMASHI is also capable of rapid charging which is a nice addition to a battery that can keep you powered up on even the longest flight or layover.
KMASHI 15000mAh MP836 Dual USB Fast Charger Ultra-High Density External Battery Pack