I rescued an equipment rack, today, and wonder if it may have been assembled incompletely (likely by grad students; I've already encountered several f*ckups)
Looking in at the lowermost part of the internals, from the front, sides removed, a "flange" (yellow highlight) is evident -- the top surface of which sits just below (~3/4") the lowest frame member (blue highlight). And, just *above* the bottom of the rack as it sits on its rollabout base.
Of course, the top of the rack is the mirror image.
This suggests one can either slip something in ABOVE the flange at the top -- and still be within the overall envelope of the rack.
Or, on top of the flange at the bottom -- and still be below the rack's frame.
Said another way, if I try to slide a battery box into the bottom of the rack, once past the front frame, it will FALL onto this flange (which makes it tedious to get out). Installing a sheet of 3/4" plywood seems to be encouraged by this design, fastening it to said flange.
Or, the bottom may be forbidden territory? and I am expected to support said box (and shelf for it) from mounts on the side supports. So, this flange may just be a fluke (or, part of another product offering that shares these parts)
Of course, there may be other intended uses; I'll start perusing photos on the web to see if I can see the interiors of the racks pictured, there.