Is there anyway to keep the battery at 80% and plugged in for battery longevity? I had an IBM Thinkpad awhile back that let me keep the laptop plugged in but at an 80% charge - my old Samsung Ultrabook did this too. Anyway to do this on a Macbook Air 11 (2015)? My Macbook spends most of its life in clamshell mode plugged in to an external monitor. It looks like you have to keep it plugged in to do clamshell mode.