Do you want to extend your laptop battery life – don’t use it! No seriously, what I mean is if your laptop is connected to the mains, then you should remove the battery to extend its life.
Why? Well when you battery is inserted in your laptop it is constantly charging. Batteries are only capable of a finite number of charges, so reducing the number of charges will extend its life. Also, by removing it from the mains it will allow the laptop battery to discharge properly when you actually use it, which will allow it work nearer its capacity.