Thanks Yow, for clearing that up. It is obvious now that she and I were confusing emergency power with backup power.
It seems that tapping into emergency power when there is so much system damage is an even higher risk.
Im not sure if Honerverse has back up power plants (cant see why it wouldnt) but it isnt normally tapped into. Unless certain sections get cut off then its damage controls job to run power and control lines as necessary. Thats not what was used here, I'm sure. Ships have backup deisels but it wont move the ship. Just ship sevices like electronics, lighting and ventalation. During most times like this the ship is dead in the water ( not moving).