The battery mystery

During the 10 days of vacation, a battery in my BlackBook died. It only went through 60 charging cycles! Well, it was constantly inside my notebook and connected to the AC, but Apple claims that charged battery is kept without further charging. I would take it out, but Apple also said that removing the battery would cause a drop in the processing power. It's quite confusing then what the user should do to avoid similar issues. In my old and loved 12" PowerBook, the battery was slowly dying - from initial 3.5 hours of power to just couple of minutes before it finally died, but that was a gradual process. In the BlackBook case, the battery died instantly, without any warnings. Anyways, I paid the Apple tax yesterday.