My HP G8 zBook Power have this feature as well, but its only accessible through bios. Luckily their BiosConfigUtility64.exe allows changing bios variables from windows, and the change takes effect immediately. My two .bats for 80 and 100% charging limits.
C:\Programs\SP107705\BIOSConfigUtility64.exe /setvalue:"Battery Health Manager","Maximize my battery health"
C:\Programs\SP107705\BIOSConfigUtility64.exe /setvalue:"Battery Health Manager","Let HP manage my battery charging"
C:\Programs\SP107705\BIOSConfigUtility64.exe /setvalue:"Battery Health Manager","Maximize my battery health"
C:\Programs\SP107705\BIOSConfigUtility64.exe /setvalue:"Battery Health Manager","Let HP manage my battery charging"