Leaving laptops plugged in all the time doesn't seem to be particularly bad for the battery, as long as (1) the laptop doesn't get too hot, and (2) you actually keep them plugged in all the time, rather than switching frequently between plugged-in and battery-powered.
My Lenovo laptop has been plugged in for the last 3.5 years, only very occasionally (once a month?) going on battery power for short periods of time. Windows reports that I still have 91.7% of the design capacity. I'm not sure if I should trust that number or not... but the last time I unplugged it, the battery seemed to last at least 70% as long as it did when it was new, so it's not totally off, either.
My Lenovo laptop has been plugged in for the last 3.5 years, only very occasionally (once a month?) going on battery power for short periods of time. Windows reports that I still have 91.7% of the design capacity. I'm not sure if I should trust that number or not... but the last time I unplugged it, the battery seemed to last at least 70% as long as it did when it was new, so it's not totally off, either.