Proker via Amazon offers its Proker Ultra-Slim 3,000mAh Extended Battery Charging Case for iPhone 7 / iPhone 8 in Black for $29.99. Coupon code "LEHP9B98" cuts that to $22.49. With free shipping, that's tied with last month's mention, $8 off, and the lowest price we could find. This TPU case adds just 0.26" thickness to your phone and features a rubber hinge design, built-in magnet, and LED indicators. Deal ends December 28.