Battery technology has come a long way from the days of having to carefully 'condition' a new battery when we first got it to maximize its storage capabilities. Conditioning is performed by fully powering and discharging the battery in succession a couple of times.
Today's laptop batteries are generally lithium-ion based (look for 'Li-ion' on the battery itself) which is far less susceptible to the traditional 'memory' and idle discharge issues that older NiCad (nickel cadmium) and NiMH (nickel metal hydride) suffered from.
Li-ion batteries represent the best power-to-weight ratio and life cycle for your personal electronics, but all batteries lose their storage capacity over time based on how they are used and stored.
Because you are using your laptop as a desktop computer, you are plugged into the wall all the time posing the question: should I remove the battery when I'm plugged in?
(Note: some older laptop designs won't power the laptop at all unless the battery is installed which makes the question pointless.)
The upside to keeping the battery installed while plugged into the wall is you get protection against a power outage. If you remove the battery during general operation, you would want to make sure that you are plugging the laptop into an external battery backup system that would keep you from losing your unsaved work in the event of a power outage.
If you leave your computer plugged in for more than two weeks at a time, the conventional wisdom is to remove the battery and store it in a cool, dry climate.
The lithium-ion battery works on ion movement between the positive and negative electrodes. In theory, such a mechanism should work forever, but shelf life, cycling and temperature affect the performance. Because batteries are used under many demanding environmental conditions, manufacturers take a conservative approach and specify a battery life between 300 and 500 discharge/charge cycles. Life cycle testing is easy to measure and is well understood by the user. Some organizations also add a date stamp of three to five years; however, this method is less reliable because it does not include the type of use.
If you plan on storing a battery for an extended period of time, make sure it has been discharged to 30-50% of capacity and store it in temperatures between 70-75 degrees. Avoid storing rechargeable batteries fully charged or fully discharged as either can cause permanent capacity loss or deactivate the built-in protection circuit.
Some folks have heard that you should store them in your refrigerator, but I would recommend against it. Humidity will reduce the life of the battery and keeping it in the fridge can introduce humidity, especially when you pull the battery out to be used.
You should always avoid using a battery when the battery itself is really cold or really hot (wait for it to return to room temperature). Heat is the #1 cause of reduced battery life, which takes us back to you using your laptop always plugged in.
If you keep the battery installed while you are plugged in for extended periods of time, it will keep the battery in a heated condition during that extended period when it could have been resting in a calm, cool, submissive state (with my regards to Cesar Millan!) thereby extending its life.
Another way to reduce the battery life is to use the wrong power pack to charge it. If you use a third-party charger that charges your battery at a higher rate than the factory charger, it will diminish the life of the battery.
For those that like to use their laptop in bed or on a pillow in your lap, you will likely be restricting the airflow which increases the operating temperature and will also reduce the life of the battery if done often.
In the end, if you simply focus on reducing the heat that your battery is exposed to whenever possible and make sure you store the battery properly, you will extend the useful life of the battery.