Just come across this 10000 mAh Ultra Slim Portable Power Bank with 2 USB ports mobile charger being sold at $4 off current price $20.99. Final price after discount is $16.99. Seems to be a good price for an external battery backup supporting iPhone 7 6s 6 Plus 5s 5, Samsung, iPad and other Smartphone.

I’ve found this discount information under special promotion listed on the product page.
Discount will be applied automatically at checkout.