Plusinno via Amazon offers iPhone 6 Plus 5.5" 2,100mAh Portable Battery Bank Case in Gold or Silver for $21.99. Coupon code "NV4GOAJJ" drops it to $16.99. Plus, Prime members bag free shipping. (Non-members can spend $35 to bag free shipping; otherwise, it adds $6.03.) That's $20 off list and the lowest total price we could find. This ultra-thin battery case gives up to 50% more battery life for your iPhone.