It wouldn't last you a plane or bus ride anyway. Battery life is like 4-5 hours at best depending on the activities that you do, could be as little as 3, and overtime, the charge will hold less and less.
That's the major problem with the PSP. I probably won't invest in one until the savvy people can figure out a way for people to create their own UMD content. The only reason I have a GBA is because I can put my own movies, books, music, and games onto it via flash cartridge.
You can do this with the flash memory, but it's limited by size and price, and also Sony cripplied the video resolution by using the same resolution as their Clie PDAs.
http://www.engadget.com/entry/1234000980024404/