An upper compact extra space can be used to set discharged batteries apart from others.
For example, a battery charger will be used when four rechargeable discharged batteries are on the upper tray.
I printed this in 0.2mm layer height (PLA SPEED MK3) and 0.3mm draft, 0% infill and without supports by using the PrusaSlicer-2.1.1+linux64.
The author remixed this model.