yeah, these batteries are lithium ion and they don't have a "memory" from crappy charging habits. So you can have the mag safe knocked off without issue. Though apple does sugguest that one calibrates about once a month. You gotta search for it as I don't have it handy, but in a nutshell you keep the computer plugged in for two hours and you can use it, then let it discharge while you use it and then let it sit for 5 hours and then charge it till full, but don't use it till its full. I believe thats how it is, but check it to be sure.
Now mine was screwy the first time I did it. The computer shut down after saying there was 5% left, but I pressed the side button and still had two lights lit up. So I started her up again and let her re-die out, then followed the rest of the steps. Now the battery seems to last a bit longer and when it shuts off on its own, it only has 1 light left of power. The battery is suposed to hold an emergency reserve, but I think mine was holding more like 25 percent instead of the 5 percent it should hold.