I use the Transcend with a battery on overseas flights just to prevent any power issues. The only downside is having to haul the battery throughout Europe without the need to use it (don't forget the plug adapters!!).

I purchased a Transcend with battery specifically for long haul overnight flights. The first time I used it was on United and I registered the device before I flew. I could not check into any of my flights except at the airport with a clerk, which was a royal pain, but at no time did any clerk ask a...