actually, you CAN remove the battery
after all, the battery IS removable.... and intended to be replaced.
But then your PPC will be on the "backup battery" and 30 minutes
later you will lose all your data. too bad.
The fact is, not only you absolutely cannot turn this thing off,
if you're down to 5% power and will be awhile before you
plug it for more power,
YOU BETTER TURN IT OFF AND TURN THE PHONE OFF
if you somehoe run down the battery to zero with a phone call,
you will have a hard reset in 30 minutes ....
this is all the result of the STUPID MS DECISION, long time ago,
not to put all the critical data/install/whatever in FLASH / SD card.