XPS15-9570: Dell Power Manager - Primary AC

I primarily use my XPS15 as a desktop, connected to dual monitors through a D6000 docking station and plugged into the AC power adaptor. I understand that I can change the battery settings in Dell Power Manager to Primary AC and it will limit my battery charge to 96%, at which point it will stop charging and power the laptop from AC power only. Is it possible to reduce the charge capacity to less than 96% (say 70% or 80%) before the laptop switches to AC only mode and stops the battery from charging? Alternatively, am I better off using custom battery setting and making the laptop stay between 50%-80% for instance but have it always run off the battery instead of switching to its AC only mode? Thanks in advance for your help.