You really do need to unplug the laptop and run it off battery at least once every few months. I've had a desktop-replacement laptop that I ONLY ran off the power cord for three years. I literally only ran it off the battery once when I first got it to see how long it lasted, and maybe two or three times when the power went out. New, the battery lasted about three hours. After a few years of never running it from the battery, I get around ten minutes of battery life even when not doing anything. It's not a big deal for me, as I always run it while plugged in, (ten minutes is long enough to shut it down safely if the power goes out), but I was astonished at how much battery life degraded.
Sure, one example doesn't mean much, but...