Comment by octo888

> fully charged battery.

Yup. Look at train tickets in England. For now it's a convenience but you'll notice the law hasn't kept up with the push to have tickets on phones: the law still says you must produce on demand a ticket when requested. So if your battery runs out or your phone crashes or the app glitches or you've annoyed the "safety" department of Google/Apple... it's entirely your problem

A moody ticket inspector is under no obligation really to give you a few minutes to sort it out