Most laptops devices these days are equipped with Lithium-ion batteries. Although these are very different to the older NiCad batteries some of the myths/misconceptions still remain.
Batteries develop a memory
False, No matter what the charging/discharge pattern is, Lithium batteries have no capacity to develop a memory
Leaving a battery constantly plugged in is bad for the battery
True, but not for the reason you are possibly thinking of. Heat is the enemy of a battery so leaving them constantly plugged in exposes them to the heat your laptop is producing which will shorten their life cycle. With regards to their ability to hold a charge see the above point
Taking my battery out will prolong its life
True to an extent, removing the battery from the heat source that is a running laptop will extend the useful life of a battery, by how much is highly debated though. If you are going to do this I recommend removing the battery at about 40% charge, sealing it in a plastic bag and storing in a cool dark place (but please see the final thought below)
Remember though your battery is acting like a UPS, protecting you from power cuts and surges. Run your laptop without one and you are unprotected. Trip over your adaptor an hour into that unsaved document and that’s an hour you have just lost!
Avoid charging the battery unless it’s fully drained
False, Waiting for the battery to be fully drained of energy before recharge does nothing to improve performance. Batteries can be charged at any time without any negative effects. There is no need to wait until the battery is flat to charge it back up to full capacity. I recommend getting into the habit of using your laptop during the day and charging it overnight, if you are a heavy user charging when you hit 20% remaining is a safe bet.
Your laptop’s battery starts dying the moment it leaves the factory, even with an unused battery expect to lose around 20% of a battery’s capacity every year from its date of manufacture. Thinking of buying a “spare” battery for use in future? Well, just save the money and buy it only when you are ready to use it.