Most modern laptops are recommended to be run WITH the battery installed at all times.
One of the main reasons, or so I'm told by a computer-knowledgeable friend, is that most laptops can't run at full processor power on just the wall power supply. Instead, the battery is used as a "reserve" to fill in for periods of high demand(which will generally be short-lived) even when plugged into the wall.
If the battery is removed, the computer will reduce the power across the board to prevent even coming close to needing the extra reserve of the battery. On my computers, I notice the loss in performance without the battery even when doing only moderately demanding tasks like watching Youtube videos.
I am a full time(PhD) student, and my laptop is my only computer. I beat on it probably 12-14 hours a day, not necessarily doing demanding work but just a LOT of reading and typing. I leave my computer plugged in most of the time, although I typically will end up doing close to a deep discharge once a week or so. I don't plan it or have a formal schedule, it just happens. My last few computers have lasted me about 1.5- 2 years each, and all of them have still had good battery life when they were retired for other reasons.
I'm told that the biggest enemy of modern batteries is heat, and that a battery that is allowed to remain relatively cool both in storage and in operation will still retain a significant portion of its capacity.
By the way, my current computer(the one I'm typing this from now) is a 13" Macbook Pro that I've been using since the end of March. The newer Apple computers don't have a battery that is intended to be user-serviceable. Apple states that the battery will retain 80% of its capacity after 1000 charge cycles, and will replace the battery if it falls below 80% within the warranty period. From my own experience, it doesn't look to me like I'll need to collect on this particular aspect of the warranty, and I don't know of anyone else who has needed to either.
