This past Christmas, my nephew gave me this awesome Anker PowerCore 20100 (model A1271) battery, which is way too heavy for backpacking, but for road or bike trips, it's pretty great. We tested it out at home and were able to charge our phones for three days (iPhone and Pixel 2). Note that you have to have a power block to plug into...it only comes with a USB cable for charging.
This was my "luxury item" on the Katy Trail bikebacking trip and it worked like a charm. Note that it was propped up pretty precariously at one of the picnic shelters and took a dive, but aside from a few scratches, it is working perfectly.
|Two phones can be charged simultaneously.|