Slightly surprised anyone needs either a power pack (or charger) today as USB ports are so readily available.
Power packs are banned from checked bags by many airlines and extending this ban to include usage on board would seem to make sense?
I routinely travel with a power-pack. It's part of my basic forward planning! If my phone dies I can have a number of difficulties and I like to listen to audio books and music from my phone on my (rechargeable) headset.
There are plenty of aircraft flying intercontinental without recharging facilities at every seat, and those that are there sometimes don't work. For a start, the KLM 747's flying to Africa (when will they be retired) have no power available at the seats.