iPhone External Battery

[BigT]

Do any of you chaps use either an external battery or battery case to charge your iPhones from?  If so whats the best? I have just tried a case from Amazon, https://www.amazon.co.uk/gp/product/B01HXNDBXY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1, total poo. Will not connect with either of the phones, usual Chinglish instructions so going back to Amazon Prime on Monday.

Suggestions Please? 

[Jake Bullit]

These work well with my Android phone and lipo battery

2S-6S Lipo to USB Power Converter Adapter w/Digital Display 5V 2A
https://banggood.app.link/Ug4zU6j0vx