I've been experimenting with my N800 to see how to get more battery life.

Heavy surfing on WiFI....it lasts about 4 hours on a charge.

Putting it in OFFLINE mode and locking the screen....battery seems to die in about 6 hours.

A question had previously been rasied in another thread if the amount of memory added had something to do with it.

My batteries started "tanking" after I added two Patriot 8 GB Class 6 SDHC cards. Maybe the memory cards have something to do with it?

I've also started watching the CPU indicator to see if there is some background task that is cycling--I found that the RSS reader application was chewing up cycles even when set to OFFLINE when I had it on 30 minute automatic update. Now I have it set for MANUAL UPDATE and I haven't noticed the CPU usage bar indicator being pegged as much.