Full cycle battery MacBook Pro Retina 13'

Do not let battery charge percentage run down to 0%.

About 20% is fine,

Newer batteries do not need calibration.

For more on this:

Macbook Pro Battery Cycle Count

http://support.apple.com/kb/HT1519

You can charge your battery whenever you can. What I do is I use my MacBook Pro until my battery goes 90% then I plug it in the power outlet the whole day. So it takes me 10 days before I get 1 full charge cycle. I bought my MacBook Pro Retina this April 2013, and my full charge cycle is 17.

It is okay to go below 20% every now and then. If you do this regularly, the life of your battery will be diminished. As standard practice, the ideal usage would be to recharge around ~40%. The main thing to remember is not to let your battery go to 0% and leave it in an uncharged state for an extended period of time. You're battery could lose it's ability to hold a charge (aka, die).

The reason you don't need to calibrate li-ion batteries is because they do not experience the "Memory effect" which the older generation of Apple portable batteries did.

As of now, there was really no need for me to use my 13" MacBook Pro Retina. The lowest was 50% with 7 hours of use. As I've mentioned, Whenever I'm just in the office or at home, I use the battery till 90% then plug it in power the rest of the day. Before when I got my first MacBook Pro in 2011, I was also very concerned with my battery. I've read a lot of posts. Then I decided i would use it till I only get 20% of battery left, and also calibrated it every once in a while, only to find out I was doing it the wrong way. So again, the best and optimal usage of the battery is to let the juices flowing, using it and charging it whenever you can.