http://www.apple.com/batteries/
One of the things it says is...
"Standard Maintenance
For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her MacBook Pro on the train, then plugs it in at the office to charge. This keeps the battery juices flowing. If on the other hand, you use a desktop computer at work, and save a notebook for infrequent travel, Apple recommends charging and discharging its battery at least once per month."
I knew I shouldn't have set my air conditioner to absolute zero...
As far as I know, the information here is still relevant: http://www.macosxhints.com/article.php?story=200303140818432...
In short:
> There is no memory and no scheduled cycling is required to prolong the battery's life.
> The typical life span of a Li-ion battery is two to three years, whether it is used or not.
> The internal resistance of the Li-ion batteries cannot be improved with cycling. The cell oxidation, which causes high resistance, is non-reversible. The electrolyte slowly eats up the positive plate and the electrolyte decays. This chemical change causes the internal resistance to increase. In time, the cell resistance raises to a point where the battery can no longer deliver the energy.
4 months later the replacement started having issues too. They tested it, found it was bad, and gave me another free replacement. That one's going on 8 months strong without issues.
I asked the tech why this was happening, if it was an issue with my laptop or something. He said that sometimes batteries go bad. It's the nature of the beast.
However, I have a friend who seems especially apt at killing the very same batteries in the very same laptop models. My rather uninformed theory is that there's a specific kind of behavior that adversely affects them - but whatever it is, I don't do it and he does. I think the key is that he uses his without power a lot, running it down frequently, etc. which seems to be what this article is suggesting (and most articles about prolonging battery life suggest).
Given my own experience, I'm continuously confused at the pervasiveness of this advice given how counter it is to my own experience - but perhaps there's some intelligence in the batteries/charger that's protecting me from myself?
I mostly think of my battery as a built in UPS and not as a gas tank.