I experienced the same dead battery overnight condition. I power down my wireless access point with my PC so there's no WiFi for the N810 to connect to unless it finds a signal from another router. One morning I awoke to the sound of my N810 loosing a WiFi signal and the battery was very low. I guessed that perhaps my N810 was on the edge of another signal which came and went causing the N810 to search for a new signal repeatedly. My solution was to put my N810 off line at night and the problem never reoccurred.