I am a content provider and providing content drains my devices like crazy. Here's my solution.
Seven years ago I bought a similar external battery pack to charge my phone and my other devices. It has served me very well over the years and it was time to find a new one. I wanted to buy a battery pack that could fully charge my iPhone 6s more than once and I came across this gem. It can charge my phone 3 times and it has a digital read out of the percentage left. I've used it to power my GoPro's, iPads, iPhones, and Apple Watch. It is about the size of my iPhone 6s so it's not too bulky and it's not too much heavier. From time to time I carry it in my pocket while charging my phone or iPad. Overall it has worked well for me and for $20 it is a solid buy.