I have just received my replacement N800 and I think I can see a difference straight away! The original just showed a little 'battery' icon when I plugged the charger in, which then dimmed but did nothing else (and I was never quite sure what Nokia meant in the instruction leaflet that says "The battery indicator bar starts scrolling on the screen after the device has powered up".) The new one showed the same icon, but was followed shortly afterwards by the word 'Charging'. Now, it never did that before! Looking good!

So it appears that something in the charging circuit in the original was u/s - either the charger or the actual internal charging circuit. I had 'sort-of' suspected that - but didn't have a multimeter to check it out. I'll leave this new one on charge for a few hours, and not be tempted to 'play' with it until I'm confident the battery is charged.

Hope this may be of help to others who appear to be having the same - or similar - problems.