Actually, I don\'t think there is a backup (button) battery inside (at least the Cxxx). When you turn it off (via power button), it\'s actually in a sleep mode for fast \"turn on\". But when you remove the battery, it can\'t stay in sleep mode and its designed to automatically reset and reboot. So if you need to pull the battery, I think its better to go to the menu and choose \"Shut down\" as opposed to \"turn off\" via power button. I know this is not a standard \"PDA\" concept... It\'s just like your desktop box.
HennaOjisan