It is easy to do this at Phantom, but I can't find the function to set up the period to start discarge  process in Mavic Air.
Does it have such option at all?

The batteries are set to start auto discharging after 10 days. Since you cannot decrease that time period, it would be best to not charge your batteries unless you're either going to use them or are trying to maintain them like this.

Hi, thanks for the inquiry. Sorry that this option is not available on our DJI Mavic air. However, the battery will automatically discharge to below 65% when it's idle for more than 10 days to prevent swelling as well. Please let us know if you have other concern. Thank you for continued support.

DJI Tony Posted at 2-7 09:46
Hi, thanks for the inquiry. Sorry that this option is not available on our DJI Mavic air. However, the battery will automatically discharge to below 65% when it's idle for more than 10 days to prevent swelling as well. Please let us know if you have other concern. Thank you for continued support.

Why ten days default?
General battery advisory by linked info directs minimizing the time ceiling voltage pressure stresses the battery,  so minimal stress time equates to charge and fly with no delay, so charge ALL episode flights the night before?
Is that benefiting the number of proper charges over the lifetime ?
What is the number of charges it can handle under proper use in craft and out of craft?

Is it imprudent to merely energize craft alone?
I run out of battery moving mp4 out from craft into cellphone cabled.
Each mp4 roughly 3.5gb five minutes flight time, takes awhile about five minutes for 44gb move.
Should i not deenergize craft battery will slump to cutoff point, which is below 30% but above some threshold.
Now, is this completely drained status ALSO deleterious insofar as reducing the proper charge number of life recharges?
The principle emphasized here is getting the most runtime out of the battery before it degenerates and can not provide rating specified.

Roughly,  any lifetime cumulative credible flight hours been professed?
Or folks continue using degenerating batteries?