Brian,
I have a 5455 and have had some of the strangest issues with the battery. I, too have woke up and found a powerless device. I have been reading a book with msreader, turned the device off, set it down, picked it up 5 minutes later, hit the power button and found a dead device. I had some real problems about 5 monts ago, my device would play a game with me everyday and wipe the slate clean on me. EXTREMELY

frustrating. I then began a regimen of using iPaq backup due to the wasted time having to reinstall everything from scratch. I considered purchasing a new battery. But now, after about 5 months, it hasn't happened again (knock on wood).
For slashlos: As for the hard reset, I think I can speak from experience, when your device appears to have completely kicked the bucket, you'll try ANYTHING to revive it. I've done more hard resets than I can shake a stick at until I "figured out" the problem with the battery.