Well we will start with what most batteries are made of and that is Lithium Ion cells (older laptop batteries were made of nickel cadmium). These batteries have several advantages including no memory and no scheduled cycling (That does not mean however that it is a good idea to repeatedly run your battery dead). These batteries are therefore low maintenance. However because their cell oxidation can not be reversed through cycling there is a definite and short lifespan for these batteries. This turns out to be around two to three years and is not necessarily lengthened by not using as oxidation goes on in the form of self discharge even when stored.

Now it is recommended that one stores the battery at about 40% capacity and in a cool place. The 40% capacity gives it the ability to self discharge slowly without going all the way dead (which is bad for these laptop batteries, if you recall). These batteries will oxidize more slowly in cooler temperatures which prolongs the life. These power cells are not meant for long term storage as already mentioned because the self discharge will drain it sometimes to the point of no return.