On my N770, the battery lasted about a week the way I use it (reading an eBook about one hour a night, screen set low, on standby most of the time).

With my new N800, it's lasting about 24-48 hours. Same hour reading.

I'm using OS2008, fully updated (including the recent update). Thinking that some software I'd installed was causing a problem, I uninstalled practically everything I'd added. The problem's still there.

My N800 is a curious beast because it supposedly factory reconditioned. It arrived with OS2007 on it, but it wouldn't work -- it booted once and then refused to switch on. After reading these forums, I inserted it into the refrigerator for 30 minutes, after which it booted, and by doing this several times I managed to get OS2008 installed, which seems to work (boots each time). I'm not sure if this is part of the same problem.