More about how I came to this conclusion and all that fun stuff below.

I have an external found this video online that shows how to use a 7805 5v regulator to regulate 9v down to 5v, then it shows how to wire it to a USB port. The end result, down-converting 9v to 5v and wiring it to a usb port, thus I could plug my cell phone into the usb port and charge or run it. This would allow me to use my PDA cell phone (in airplane mode) to watch video's for the 13 hour flight. However, I read that the linear voltage regulator like the 7805 isn't very efficient, and it may have a max output of 500mah without a heatsink or something. My cell phone draws closer to 1000mah/1A, so I'd need a heatsink. I read it's about 43% efficient, wasting a lot of energy in the form of heat. Then somebody recommended a switching voltage regulator instead of a linear one, so, I found and purchased this one on EBay. Sounds simple enough, pay a few dollars more and get a more efficient converter. It also appears to be able to handle 1A or 1000mah of power without any problems. Sounds good. Question though, the listing says "It is recommended to put minimum of 100uF capacitor across the output voltage to ground (ideally 330uF)" well, that statement confuses me a bit. I have a rudimentary understanding of capacitors. Will I not be able to wire up this "3-Terminal 5V 1A Switching Voltage Regulator Power Supply" like the 7805, do I require additional components? Thoughts? Also, this is what got me thinking, I believe I understand a little bit more about how cell phone car chargers work. They simply have one of these voltage regulator chips inside them to down-convert 12v to 5v. Now from what I'm reading, the Linear 7805 and the switching voltage regulator's will accept any voltage above 5v up to 40v. So 12v car power would be fine. But wouldn't a 9v external battery such as mine equally be ok? If I didn't go nuts and build this crazy rig, couldn't I simply adapt a car charger to work with my external 9v 5400mah battery? Would a simple car charger take 9v just as much as it'd take 12v?

Lastly, I wonder if Car Chargers use the Linear voltage regulator (cheaper) or the more efficient switching voltage regulator.

btw, I have an ATT Tilt phone, aka HTC Kaiser. It has a mini-usb charging port, much like the RAZR's and other common devices. The charger it came with puts out 5v / 1a. I'm also wondering if I should have the battery in the phone when I have it connected to the external battery. Doesn't make sense to draw more power charging the phones battery and running the phone, vs just running the phone. Seems like it'd draw less power, giving me more run-time. I have 3 8gb microsd cards filled with video's, gotta survive the 4h flight across the U.S and then the 13h flight across the ocean, and back again later.