"I can't for the life of me guess what this thing was..."
"The closest room to the entrance had this piece of ancient machinery..."
That looks like a run-of-the-mill standby generator. The electrical generator is the horizontal cylindrical lump at the left. The three orange/red canisters are probably oil filters (Fram replacement cartridges, perhaps?) The radiator is to the right, with a ducted cowl to exhaust the hot air. I'm guessing that the engine exhaust stack pokes through the wall and has a series of silencers attached before poking out of the ground somewhere above. That's my (mostly) educated guess, based on the clarity of the photo.
"...a room with a workbench, electrical panels and many banks of what look like telephone switches."
This indeed looks like a phone room. But instead of switches, these are probably just wiring terminal blocks. When multi-line phone cables terminate in a central location the individual copper pairs are spread out on across orderly arrays of terminals, and then short jumper cables are used to patch circuits from one pair to another. There may have been additional switching gear in this room at one point, but it was probably removed for scrap.
"... the ancient jug of water sitting on this fuse panel..."
My guess is there used to be a back-up battery system near the cable room in img020 to power the phone equipment. Almost all phone gear runs on 48V DC, and inside any telco central office you'll find a bank of batteries (in addition to the generators) to keep the system alive during power failures. The water jug in this photo may have simply been distilled water used to top up the lead-acid batteries.
"I assume the initials mean 'Southwest Battery D_____'"
Date: Fri, 15 Oct 2004 20:07:28 -0700
Great posting and great website of pictures!
I hate to break it to you, though, but SWBD in an old acronym for "Switchboard", which fits in the context of where you saw it. Thus, I doubt that the place was called Southwest Battery D___.
[Note from email@example.com: I was wrong about the abbreviation 'SWBD' but I'm sure Battery D_______ is the name of the place, it's listed on a nearby map.]