Sunvalleytek via Amazon offers its Prime members the RAVPower 3,200mAh Luster Mini External Backup Battery Pack in Black, model no. RP-PB08, for $12.99 with free shipping. (Non-members can spend $35 to qualify for free shipping; otherwise, it adds $6.18.) That's $17 off and the lowest total price we could find. It features a built-in flashlight and compatibility with a wide range of devices (including the iPad, iPhone, and Android phones and tablets).