Nowadays, almost all new laptop use lithium battery compare to decade ago where nickel battery widely used. Lithium battery is a lot better than nickel since lithium battery doesn’t suffer from memory effect. Do you remember that one good way to prolong mobile phone battery is by only charging the battery once the battery power nearly empty. The advice is due to most old mobile phones use use nickel battery that suffer memory effect. Let say that you charge your mobile phone although 40% battery still left. If the mobile phone use nickel battery, then you might having trouble as the nickel battery will forget that there is already 40 % charge left once charging start. That means, your mobile phone will show empty sign once you have use all of the 60 percent charge.
This is totally different if your mobile phone or laptop use lithium battery. Since Lithium ion battery doesn’t have memory effect, it doesn’t matter anymore when you charge your laptop battery. Besides free from memory effect, lithium ion battery knows when to stop charging once it is already full of charge. This avoid overcharging from happening in laptop battery.
If overcharging never happen, then why some people recommend to keep laptop battery away if they want to use plug-in power? That is nothing related to overcharging but due to heating problem. Lithium battery can be worn out faster if it is left in hot environment. Thus leaving the battery in the laptop while using plug-in power is not a good idea for someone who make laptop as desktop replacement as the battery can become hot easily.
A good practice to keep laptop battery is by putting it inside plastic bag and left it in a cold and dry environment. Once in a month, put back the battery inside laptop and use it so that the battery will always perform at it best.