Sunvalley Brands via Amazon offers the RavPower Ultra-Slim 10,000mAh Quick Charge 3.0 Portable Power Bank in Black for $29.99. Coupon code "NPBNV9KN" cuts the price to $19.99. (White also drops to this price after coupon.) With free shipping, that's a savings of at least $10 and the lowest price we could find. It includes two ports. Deal ends July 31.