This photo (follow link) shows the cover as well as the box. Clearly the cables shown connected to the battery in the open box constitute a test harness. The way the real cables come out of the box is much different.
And yes, replacing the battery inside the box will be much more difficult.
From what I can see the plastic cover and the steel one are identical in form. A harness leads from the battery to a terminal on the cover to which a further harness is attached.
I wonder how the case will be vented?
Replacing the battery - about 40 additional screws to undo. Unless - perhaps - the LRU will be the battery and the case.