I am not sure but it could be the battery drain issue reported by some people. My N800 (OS2008 installed) barely gives me 24 hours with a single charge and that also if I don't use it in that period. Wifi is connected during this period with google talk and a SIP account active. (Running Skype also sometimes).

Thoughtfix's blog:
http://tabletblog.com/2008/01/os2008...ery-drain.html

Or perhaps when your wifi got disconnected, your tablet was trying to re-connect/search for the access point continously which eats up battery?

You could also try run "top" in xterm to see if there is a process eating up CPU cycles extra-ordinarily.