Why would you open the laptop screen when there is no battery? The only time when you have no battery in the laptop is the few seconds it takes to replace one with another.
AFAIK, fixed batteries are located in the very same place as the removable ones: at the rear of the laptop. They are not spread everywhere, there is no hyper-advanced design is that respect, and they definitely do not occupy 60-80% of the chassis. They could be pulled away / inserted back from the rear is the design choice was such.
> AFAIK, fixed batteries are located in the very same place as the removable ones: at the rear of the laptop.
Not typically. The tiny system board lives near the back of the laptop, to connect to the ports and the screen. (Often, the system board doesn't even take up the full width of the back of the laptop, and instead has ribbon cables connecting the ports on one side to the system board.) The battery takes up all the space under the front and middle of the laptop.
> They are not spread everywhere, there is no hyper-advanced design is that respect, and they definitely do not occupy 60-80% of the chassis.
I've seen the insides of many laptops, both in person and via pictures. I've seen battery cells laid out in many different shapes around the system board and other components, including Ls, Us, and Hs, and in multiple packets of cells with minimal connections between them.
As for "advanced design", https://www.apple.com/macbook/design/ made a point of talking about its terraced battery cells to fit the enclosure. And while some laptops might not go that far, I've seen many laptops shape groups of battery cells around other components to make a non-rectangular battery.
And as for volume, I've personally seen the internals of many laptops, and the better the laptop, the higher proportion of the volume that consists of battery cells. I wouldn't have given those estimated numbers if I hadn't seen laptops fitting both ends of that range and various points in the middle. (Some quick searches suggest that much smaller laptops, and lower-end laptops, may dip as low as 40-50% battery cells; medium and large laptops, and those intended as higher-end or with higher expected battery life, have more.)
AFAIK, fixed batteries are located in the very same place as the removable ones: at the rear of the laptop. They are not spread everywhere, there is no hyper-advanced design is that respect, and they definitely do not occupy 60-80% of the chassis. They could be pulled away / inserted back from the rear is the design choice was such.