I think they are useful. I went to LA with a friend in Aug, we were low on battery and needed the phone badly for calling uber and navigation. we were in a mus

I think they are useful. I went to LA with a friend in Aug, we were low on battery and needed the phone badly for calling uber and navigation. we were in a museum, and they have charging boxes ... basically a passcode secured lockers with cables inside. We had to wait for 10 minutes for the phone to reach 15%. it would be nice if it was a battery that I could carry while touring around the museum.