I've been careful to use my laptop off the charger almost every day (i.e. avoiding keeping it at 100% all the time, particularly when warm), and it's only in the third year that the capacity has started to drop a bit (I used to get 5 hours active hacking capacity, now it's more like 4 1/3). The old battery, on the other hand, completely died within a year after being kept 100% charged all the time. However, I try to avoid deep-discharging the laptop. In my experience that'll kill capacity quickly (I did it once with my phone and it's never been the same after that).