When should I charge my MacBook Air??

In theory, you should be able to start charging it whenever you want, but make sure you charge it fully before unplugging it. Normally, users wait until battery percentage is low (20% or less) to start charging a MacBook.

Another option is to always use it plugged, unplugging it at least once a month to make a battery cycle. See > http://www.apple.com/batteries/notebooks.html

can i use my mac air while charging?

youre worrying for nothing really.

LiPo batteries dont need conditioning, but optimal "out of the gate" on new cells indicates (from the battery gurus) are that first 10 cycles or so dont drop lower than 30-40% before charging. Same reason new cars are all indicated engine break in you dont "peel rubber" and drive crazy for the first 100 miles or so.

rough treatment on LiPo cells has only be found QUANTIFIED in one area: often dropping the cells at or near 15% or less percent. Key word being "often"

The only rechargeable cells more reliable than LiPo cells in your Air are in million dollar satellites circling the earth.

To parrot what I said about the ONLY thing to avoid in the LiPo cells as per often dropping them very low is from the battery gurus to which I quote:

Li-Ion and LiPo are subject to aging, even if not in use — storing the battery in a cool place and at 40 +/- percent state-of-charge reduces the aging effect.

Ideally charging at 20-30% but as little as possible dropping sub 15% +/-

Thank you. I feel much better :>)

LiPo cells (lithium polymer) cells (as in your Air) dont need conditioning. however....

LiPo cells DO NOT LIKE being often dropped to sub 15% range.

Many battery Gurus indicate that LiPo cells when new in a device should be the first 10 cycles or so NOT be dropped sub 40% range before recharging.

Hi, thanks for the help with my screen saver problem. I just noticed this thread and wanted to know this: I just bought this MBA and it has been charged from about 10% about 4X so far (at the direction of the Apple guy who sold it to me). If I continue charging for the next 6-10 cycles as you suggest, at 40% and above will that help the future of this battery or have I just defeated any goodness that this could have done???? I asked many people at the apple store how to treat this battery as I have had problems with batteries on PC's and this was one of the reasons why MBA's sounded so attractive to me (besides a general "I've had it with windows" attitude). Any advice on proper battery care and management is greatly appreciated. Even the apple support phone people seemed to have no clue. Thanks.

certainly yes you can.

just dont leave it on charge all the time. off or on.