From my understanding, the requirement for the battery back up is with the State's Public Utility Commission (or whatever it's called in each state), but that is for systems where the MTA is NOT being powered by the tap and is using wall electricity to power itself.
The issue was raised when the question was asked, "How does a Cable Digital Phone Customer call 9-1-1 when the power has gone out in the neighborhood?".
If the MSO has not, will not, or cannot answer that basic question, then there is trouble in that MSO's future.
Good Luck with this one.
RadioMan