Should laptops remain plugged in when their battery is 100% charged?

This page has a good answer: "it depends"

The answer is: YES and NO, it depends on the situation.

Having a battery fully charged and the laptop plugged in is not harmful, because as soon as the charge level reaches 100% the battery stops receiving charging energy and this energy is bypassed directly to the power supply system of the laptop.

However there's a disadvantage in keeping the battery in its socket when the laptop is plugged in, but only if it's currently suffering from excessive heating caused by the laptop hardware.

So:

• In a normal usage, if the laptop doesn't get to hot (CPU and Hard Disk around 40ºC) the battery should remain in the laptop socket;

• In an intensive usage which leads to a large amount of heat produced (i.e. Games) the battery should be removed from the socket in order to prevent unwanted heating.

The heat, among the fact that it has 100% of charge, is the great enemy of the lithium battery and not the plug, as many might think so.

From a view point of your battery's health you should keep the laptop plugged into the wall and unplug the battery from the laptop. Not because of over charging or whatever, but because of the heat generated by the laptop. By removing the battery it will be cooler, which is good for the battery.

If you were to unplug the laptop from the wall, you would start to drain the battery, and would have to recharge it later. Since the limiting factor on laptop batteries (all rechargeable batteries, actually, that I know of) is the number of times they can be charged and drained, any time you can avoid draining the battery will make it last just that much longer.

This all depends on the type of material the battery is made out of. Each battery material has different ideal characteristics. Look on your battery label and determine the type of battery it is. (i.e. lithium-ion (Li-ion), nickel-metal hydride (NiMH), nickel-cadmium battery (NiCd), etc. Once you determine which type of battery it is simply google the material, and read about the capabilities. This should tell you all and more of what you would like to know.

A note on charging.. Not all charging circuits are created equal, so if you have a deficient charging circuit, you might indeed want to unplug the battery after it has been fully charged like was suggested above.