Industrial AT System

I originally bought this Advantech industrial system because I wanted a compact AT case whose side panel(s) can be removed rather than taking off a U-shaped cover which takes up more space.

If I had a selection of SBCs, keeping the ISA/PCI backplane installed makes sense. For now, however, I have a Soltek SL-54U(5?) Super7 board installed. There was a punchout for an AT-style keyboard port, so I should be able to use almost any Baby AT-style board.

I like the AT-style backplane and would like to reinstall it when/if I get more than one SBC.
I was surprised to find a remarkably heavy 5.25″ bay-mounted lead acid battery connected to the ATX power supply. The PSU fan keeps running even when off- maybe has to do with charging the battery.
There was a punchout for an AT-style keyboard port, so I should be able to use almost any Baby AT-style board.

IDEAS:
486 (on hand: Biostar 84??33UUC-A, MSI MS-4144)
Socket/Super7 (on hand: P5A-B, GA-5AA, GA=
Slot1/370 (nothing on hand)