Do NOT fully decharge Lithium-Ion batteries! Deep-cycling is intended for NiMH and NiCd batteries. Li-ion batteries lose capacity every time they're decharged.
They also lose capacity over time, about 15 to 20% a year, that's inevitable. When the battery is often kept in warm environments, this percentage is higher. This percentage also depends on the charge. The higher they're charged, the more capacity they lose. Therefore, when Li-ion batteries aren't discharged often (or kept in storage), it's best to have them charged at around 40%.
Therefore keeping it charged all the time (eg when you always connect your 'book to net power), is not optimal!
BTW, when storing a Li-ion battery, keep it in a refridgerator!