I always worked with my laptop online, with battery on it. (4 years old now) I used the battery only in airports and in some rare occasions. The battery still have the full capacity, it provide energy for 2 and a half hours, like new.. The number of cycles affects, not keeping on the laptop when online. And if you don't discharge it completely, the effect of aging is even lower. It's true that the battery lose capacity over time even if is not really used, only kept on laptop, but this is really not a concern, because the rate is maybe 5% per year. Temperature is the real problem, but as long as is no more than 26-27 degrees, it's still okay.