An external battery for charging your laptop and cellphone on a long flight seemed like a good idea. I almost clicked on the buy button, but then I realized In most cases, I wouldn't use it for work. It's just to keep myself entertained on the plane. Well, I can still avail myself of the old reliable solution of reading a book.

The only remaining argument is that I could use the external battery even when I'm not on a trip. But then portable batteries are not designed expressly for that purpose...