I'd like to run the N810 off the charger for long periods, but the manual says it's a bad idea:

It seems strange that the N810 wouldn't have overcharge protection circuitry. Is that really the case?

This travel charger for Nokias has a charge indicator light and claims to have overcharging protection. Why would a $2.99 charger have that and Nokia not?

Lies. That info actually applies to NiMH. The problem with leaving li-ion batteries plugged in for long periods is from heat, but the NITs don't generate much heat, so it's not really an issue.

I leave my 770s and my N800 plugged in most of the time when I'm at home, and haven't had any major impact on battery life.

The device has both overcharge and undercharge protection built in, and Nokia chargers are some of the best. Don't buy the aftermarket garbage.

Well, there it is.

The General has spoken.

the general is awesome. a great asset to this forum indeed!

Lithium ion/polymer batteries do loose capacity at a faster rate if they are constantly "topped off", which is what happens when you leave the device plugged in for a long time. It charges to 100% and then stops. As soon as the battery goes to 99%, it starts again. This repetitve cycle from 99% to 100% is actually worse than, say, 80% to 100%. That said, the real-world impact is small. Rougly speaking, if a battery has a 3 year useable lifetime, it might diminish to 2.5.

well I don't know about the n810 but all the laptops
I've ever owned won't start recharging unless the battery
gets below a certain value (90% or 95% on two I've had).

Is it true that the n810 constantly cycles when plugged
in and recharges from 99%? I hope not.

That raises another heat question. I also bought an external charger so I can carry a spare battery. Before the charger cuts off, the battery gets warm for ten or fifteen minutes. Is that enough to damage it?

No, and it's normal.

I should probably clarify my heat comment a little bit: this is heating as compared to a laptop. Most modern laptops tend to become thigh-scorchingly hot while in use and during charging. The amount of heat generated in a laptop in-use and charging will have a strong effect on the life of the battery.

We don't generate the same sort of heat levels (not even in the same ballpark) in our ITs as a laptop, so the effects of leaving it plugged in aren't nearly as strong.

Honestly, estimating the life of the device at something aronud 4-5 years, I would just go ahead and use the battery in whichever way worked best for me. At worst, you're gonna drop $30 for a replacement battery a couple years down the road if it goes bellow your acceptable power levels, and at best, you'll go through the entire life of the device without having to worry about charging cycles or when to plug or unplug your device and still have an acceptable power level.

Maybe the n810 has a better charging algorithm, but the n800 starts charging as soon as you plug the charger, no matter if the battery is at 20% or at 99%, at least that's what the battery applet seems to show.

... but it quickly notices that it is fully charged and doesn't charge after that.

I am one of those that keep my NIT plugged in most of the time (I keep it plugged in overnight every night, when I am not using it and use it while it is plugged in in the morning). I have noticed that the charging status indication is pretty smart (it will not keep saying "Charging" when it is done) and any degradation is below my perception threshold.