I didn't see it mentioned but putting your N810 in the supplied case and placing in your pocket repeatedly activates the display when anything is pressed against it.
I had my go dry one night after a full charge. I discovered that there are some WiFi access points in my area that are far enough away that the signal fades in and out. I noticed this because of the connection lost sound and the fact my N810 is next to my bed playing additional duty as alarm clock. I've started leaving the device on but setting it offline so WiFi wouldn't wake it up and it wouldn't look every 10 minutes. It may be a coincidence but I haven't had the low battery over night problem. [I could of course power down over night because the alarm still wakes the N810 up to sound off. Perhaps there are additional causes that result in this symptom. I only know what seems to work for me.