My N800 has been in use for a year. My machine reports battery time left 9 days at idle, 6 hours in use (that is with Bluetooth headset paired and WiFi connected). I have two SanDisk 8G SDHC cards inserted.

I cannot say what the actual "drain time" is before I need to charge it for I usually leave it plugged in when ever I am near a convenient outlet. I have a 12VDC cig. adapter in my car because I'll play music in the car from the N800 and use it with a bluetooth GPS rcvr while driving. Not cycling (draining) the battery needlessly will extend it's overall life.