LAPTOPS CAN EXPLODE! Leaving the battery in your laptop all the time while keeping it plugged into the wall all the time is bad! It won't overcharge but heat from the computer wears it out. And being 100% charged for years also wears it out. It is best, if you are actually using the battery, to keep it charged at 40%-80% at all times for longest life.
On rare occasions batteries have even exploded like the defective on in the video below. For more tech tips see my West Hollywood Computer Repair website http://wehocomputerrepair.com/blog_posts_main.htm/