ATC via Amazon offers Prime members the Lumsing 8,000mAh Li-Polymer Portable Power Bank in four colors (Black pictured) for $14.99. Coupon code "7IAHQ9SB" drops it to $9.99. With free shipping, that's a $5 savings and the lowest total price we could find. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $6.33.) It's compatible with most smartphones, tablets, and other USB devices. Deal ends March 31.