I think the battery just powers the pumps that push the fuel into the combustion chamber. But it still runs on refined dinosaurs.
Even so, not having to burn fuel to spin the turbopumps is potentially pretty big.
The fuel pumps in an orbital rocket use a lot of fuel that doesn't directly contribute anything to thrust. This results in a significant reduction in Isp, which you basically can't have enough of.
The Russian RD-180 engine that powers some of our launches today uses a system that "recycles" the fuel pump drive turbine exhaust into the main engine's exhaust stream, thereby recapturing some of the work lost to the task of pumping fuel into the combustion chamber.
The RD-180 accomplishes this, but at a price: the turbopump engine has to operate at engine chamber pressure, which puts it under a lot of additional stress. RD-180s have been known to blow up on the launch pad. IIRC, they are not "man-rated," largely for this reason.
LOL! Great turn of the phrase.