Hi everyone I have been reading this thread with lots of interest. I seems to go against my experience and understanding of lithium ion batteries. I have always kept my battery in an kept it charged up >95% whenever I can, and I lose about 10-15% of the capacity per year. My understanding is that (contrary to what's been discussed) to maintain a lithium battery in maximum longevity, you should charge frequently, and keep it topped up. Overcharging does kill the battery but this is not a problem with modern 'books because of their more sophisticated charging circuits. Deep discharges cause more damage to capacity than small discharges. Wikipedia has a succinct article on batteries http://en.wikipedia.org/wiki/LiIon as does battery university http://www.batteryuniversity.com/parttwo-34.htm In summary A) Every lithium battery degrades over time B) Temperature is by far and away the largest cause accelerating this degradation C) If you are going to store a battery, take it down to 40% and pop it in the fridge (NB one of the problems is how you keep this maintained at 40% as the battery will lose charge continually); Apple actually recommends you fully charge the batteries then pop it in a cool place (http://docs.info.apple.com/article.html?artnum=10571) D) Recalibration of the battery should be done periodically by using the book until it goes to sleep, then recharge fully (http://docs.info.apple.com/article.html?artnum=86284) E) Frequent small recharging is less harmful than large recharges Rgds Khoo Steve Jobs on Bill Gates: "I wish him the best, I really do. I just think he and Microsoft are a bit narrow. He'd be a broader guy if he had dropped acid once or gone off to an ashram when he was younger" (From a 1997 New York Times interview)