I purchased this Selectec external power bank for charging my iPhone and my Fitbit, when I am away from a power source, or if it isn't convenient to use a power.

Source. This Selectec power source, is 8600mah, has 2 USB ports, for charging two items at one time, and has LED indicator lights, so you know how much of a charge is left. Tonight, I charged my iPhone and my Fitbit at the same time, to see how well this power bank worked. I must say, I was quite impressed. When I plugged my iPhone into the power bank, my battery was at 28%. My Fitbit battery light was flashing, and it was no longer giving my the time, which is an indication, that it is ready to shutdown. I plugged both items into the power bank, and charged them for 60 min. At exactly 1 Hour, my iPhone battery was 72%, and my Fitbit was showing approximately 75% charged. The LED indicator lights on the power bank were all 4 still lite up,which shows that there was still over 75% charge in the power bank. I was using my iPhone the entire time that it was being charged, which makes this even more impressive. This will be great to take along, when I go to DisneyLand the next time, and am away from the motel for 16+ hours during the day. It is about the same size as an iPhone 5 or 6, so will easily fit in a pocket, just like your phone does.

Product link: https://www.amazon.com/dp/B01I31ZL5G/