A lot would probably be an understatement. Aren't most batteries in data centers designed to just hold load for seconds or a few minutes at a time while generators start up?

If the problem is an instant disconnect of a large load, switching that large load into charging batteries at that instant, for a minute or so, feels like a solution.

Yeah, different batteries, different purposes.

Keeping the data center up is completely different from keeping the grid up.

Not only are the batteries too small; they're also on the wrong side of the disconnect.