I have read the minis overheat if turned on and sitting for some minutes, engines on or off. These drones don’t have a cooling fan.
It’s stated in the manual
Better to not completely deplete any Lithium battery. 20% remanent at landing is good and after flight recharge them to 55 to 65% for storage and you will always have healthy batteries.
My Air 1 was bought December 2018, that means it's now 4+ years old and the batteries are still doing well. I do store them at 55-65% after use, and have never go below 30% on them.