1) OK, I took the battery out plug-in the power, N800 will not come on.
2) I not to sure you can assume you can over charge the battery.

You are more brave than I am. Thanks for that. I think I will try to run it with battery in and on mains power and see if it switches off eventually. Then while it is charging I will see if I can switch it back on. If so then I could just leave it like that and it should stay on forever. (I hope )

I use it a lot while it is charging. Mostly remote via ssh and vnc. Not problem and no reboots.

That answers my question. Thanks.

How about putting the charger on a timer so that it turns off for a couple of hours, say, twice a day? Like Karel, I don't think that overcharging is a potential problem (though I'm only going by what I read somewhere, which may not be reliable). On the other hand, I believe it is bad for the battery to keep it fully charged all the time, hence my suggestion of a timer.

Alternatively, you could just turn the power off every now and again when you think of it, and turn it back on when the battery has run down to about 40%. (That's what I do with my notebook.)

I'm one of those saps who actually think that Wikipedia makes mostly sense, so this is where I got the mustard:

http://en.wikipedia.org/wiki/Lithium_ion_battery

There are basically only two things that will damage a Lithium-Ion battery: prolonged storage without any charge, and age. That's right: Li-ion batteries have this in common with us humans that they start dying from the day they were made.

There's more interesting reading on that page, but the main thing is that a fully charged battery at room temperature will die sooner than a half-charged one in the fridge.

If it doesn't explode, of course...

Li-Ion cells like the one in the n800 are a very sophisticated brand of battery, as it actually features its own charging/safety circuit. What it does is cutting the charge when the battery is full, and waiting until the battery is drained enough to begin charging again. This was not the case in the old days with Ni-MH technology, as they where not subject to such extreme consequences when overcharged. Therefore the Ni-MH where generally trickle charged because of a, in most cases, "dumb" charger. My point is that a Li-Ion battery does not take any harm from being mildly recharged now and then, because it has no real memory effect. Which is again a trait of the old Ni-MH technology. It can however be dangerous to use non-authorized Li-Ion batteries as they are probably not subject to same tests and standards as the originals. Furthermore the charging circuit might not be as efficient as the original, and that can lead to overcharging and consequently explosion! I am not sure about he "fake" battery but i think it would be difficult to cheat the charging mechanism. A recommended read is:
http://www.batteryuniversity.com
It's an extensive resource for battery knowledge and care.

Even though it can't be overcharged, the lifetime of the battery is slightly shortened if it stays on 100% charge _at all times_. At least in combination with some heat.

That's why laptop batteries simply don't last at all if you keep them on the mains all the time -- they're a bit warm inside, as well as being at 100% charge.

Lifetime is drastically improved if it's a bit cooler though, so it's not as bad as that for a device like the N800.

More on this on the batteryuniversity link in the posting above.

This is fascinating stuff. I never expected so many posts. I think that the idea of switching the mains off periodically is a good one. The timer is too. By the way, the battery is lithium polymer not lithium ion. Is there any difference between the two?

from the website which so many of you have quoted above, a few things are learned:

1. You cannot overcharge a modern Li-Ion battery. They are designed to stop charging once full capacity is reached.

2. Discharging a Li-Ion battery too much will kill the battery. However, there is protection circuitry installed to prevent that as well.

3. Charging a Li-Ion battery more frequently is better than charging it less frequently, as can be seen by looking at the battery lifetime / charge count chart. The battery capacity is shortened if you wait too long to charge it.

4. Li-Ion batteries do better in cooler ambient temperatures as it prevents nucleation bubbles.

My suggestion, based on the facts is to use the battery that came with your device, and keep it plugged in. There is probably a circuit which is broken when you disconnect the battery, so making a fakie will likely fix that, but then you'd have the device trying to charge the fakie all the time. You wouldn't want that! If it's inside, hooked to the mains, in AC you will be fine.

If you are good at making electronics, your best bet would be to remove the battery, disconnect the charging port, and wire up some leads to the battery terminal which will give you the proper voltage and amps ( 3.7v / 150mAh ).