I have been using my N800 fanatically for a year now and my Nokia battery and my two cheapo Hong Kong batteries have not needed to be replaced yet. I hardly ever plug in the N800, almost always just switching batteries.

Battery life of course depends on what you use it for. I use mine for web access, for listening to audio, and for reading (Fbreader).

I have never had a fully charged battery last for only an hour, even the cheap Hong Kong $10 batteries.