When it comes to the grid, there's a lot of outdated information left over from the 20th century, so any web search for "system interia" needs to also include some searches on "grid forming inverter"' to make sure that the info is complete.

(And "reactive power" could be good too but not absolutely necessary to understand at first...

This is what batteries can provide very well.

I understand the concept. I was asking for a cite about the seemingly-incorrect point about batteries. FWIW, that very search term doesn't produce the string "battery" anywhere on the first page.