That is not how GPU multiplexing works on Laptops. My dGPU most certainly works on battery, though I can directly disable it if I like (or use a power saving power plan).
For example, I could disable the nvidia card on my ThinkPad W530, but then i'd lose the use of the external video output (because it was wired to the nvidia card).
and yes i know it depends on whether the laptop has a mux or not... it's not always easy to determine, not all reviews go explicitly over this detail...
I just don't want a discrete graphics card. Not an nVidia one for sure.
It works, but it sucks power like no tomorrow if it actually stays on. Its basically unusable if you want more than hour or two of battery life (or you use it in short bursts for compute).
