Hi, Yes they certainly do drain the battery. You might run an app like juice defender and turn off things you don't need to run. Set it for checking the web, email and such every 15 minutes and it may help. It should be possible to run the mp3 part with the screen on minimum and nothing else going.
Thanks for the tips. I'll definitely give them a try, and I have also found the second (spare) battery that came with it. It's worth carrying that as back up on longer journeys I guess.