Just got back from detroit. I took my Sony D25-S with me.
1. My bag with my sony, and my external battery pack was always searched. ( my battery pack was in a rat shack project box, mad with a 9.6v rc car battery. I guess it looked suspecious to the xray machine.)
2. suprisingly, once up in the air, it didnt skip, listening with my etys.
3. my "battery pack actually lasted about 12 hours .
4. If flying , yes you still can listen to it in flight.
5. I would reccomend that you tell airport security about any diy amps or battery packs, to avoid hassles.