The ware would most likely come from someone that has a spare battery that is ready to go. Think of your phone burning 80% of the juice and you’re about to hop on a flight that you’re barely going to make (no time to charge). Slap that stand by battery in and off you go. That’s what I did with my old Nokia or blackberry back in the day. Oh and for my HTC aria.
Sounds stupid, arent there charging ports on planes?
And other than plane where external battery is an issue, i just have a small brick that connect to my phone by the magnets on the back and wireless charges it, this is only really needed if you are doing something all day on the phone, like going around a city, taking pictures