eCase via Amazon offers Prime members the KMASHI Mini 2,800mAh External Battery Pack with Light in Black or Hot Pink, model no. KMAX-807, for $9.79 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $5.22.) That's $16 off list and the lowest total price we could find. It's compatible with devices that charge via USB and purports to provide 1,000 charge/discharge cycles.