Having selected and purchased several UPS systems with price tags up to about a quarter million bucks, I don't know where I would find a corporate battery UPS with anything but lead-acid batteries.
Lead-acid in this application is ubiquitous. It it wasn't, I would have specified.
The fact that someone reinforced the floor system sure looks like they put in a large, heavy UPS system. That would have lead-acid batteries.
This was the corner of the floor where we saw molten metal flow from.
Every PBX in WTC would have has a lead-acid UPS. You don't have a clue what I am talking about.
And I wonder how much sulfuric acid is in that UPS. That area would be past the boiling point of sulfuric acid, wonder what the volume of sulfuric acid vapor would be.