TechRabbit offers the Surgit Battery Case for iPhone 7 or iPhone 7 Plus in several colors (Black pictured) for $29.99. Coupon code "TRSRG15" cuts that to $14.99. With free shipping, that's the lowest price we could find by $13. These cases feature rubber bumpers and 3,100mAh and 4,00mAh batteries, respectively. Deal ends September 18.