I notice a big power drain after installing an 8gb SDHC card. With that slot empty, my N800 can go a couple of days without recharging. Simply putting the SDHC cart is seems to cause a massive power run down.

I strongly agree with many posters when they say that high CPU usage does burn up the battery. Running the web browser almost always burns the CPU at 100% these days, especially when reading the active java sites (gmail). This web site uses a lot of CPU, incidentally.

Somtimes I spot "runaway" processes that may be churning away for no good reason. I've been keeping track of applications that are using a lot of CPU and in the terminal I run "top" to see them. Sometimes, there is a program running taking tons of CPU with a vague title like "sh" but no details. I shut down the system all the way, and restarted, that sh program was still there. I reasoned that if the N800 is trying to do "session management" then some bad program that was running before will get launched again. But I don't know if that's what it is doing. I know on Linux lots of systems do have session management. After gaining root, I find that "kill -9 nnn" for the process numbered nnn does kill the mypsterious high CPU using program "sh".