ATC via Amazon offers the Lumsing 13,400mAh Portable Power Bank in Black, Gold, or Silver for $23.99. Coupon code "2HQF2MS4" cuts it to $13.99. Plus, Prime members net free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $6.48.) That's $46 off list and the lowest price we could find. It's compatible with most smartphones, tablets, and other USB devices. Deal ends April 24.