Romoss Direct via Amazon offers its Romoss 8,000mAh Battery Charger Case for iPhone 6 Plus / 6s Plus in Black for $27.99. Coupon code "ROMOSSEC" cuts that to $20.99. With free shipping, that's $7 off list and the lowest price we could find. This case allows charging and syncing with your original Lightning cable, and features an automatic shutoff.

Also available is the Romoss 3,800mAh Romoss 3,800mAh Battery Charger Case for iPhone 6 Plus / 6s Plus for $19.49 via the above coupon. With free shipping, that's $7 off list and the lowest price we could find. It has features similar to the above case. Both deals end January 15.