XREXS via Amazon has 4000mAh iPhone 8 / 7 / 6 Plus Rechargeable Charger Battery Case (5.5 inch) for $18.89 when you apply the code: XREXSSD2
The code is also available for the iPhone 8 / 7 / 6s / 6 Battery Case ($16.99 for the 4.7 inch)
XREXS via Amazon has 4000mAh iPhone 8 / 7 / 6 Plus Rechargeable Charger Battery Case (5.5 inch) for $18.89 when you apply the code: XREXSSD2
The code is also available for the iPhone 8 / 7 / 6s / 6 Battery Case ($16.99 for the 4.7 inch)