According to the FCOM (
A318/A319/A320/A321 FCOM 1.21.20 P7):
To prepare for ditching, the flight crew must press the DITCHING pushbutton on the CABIN PRESS control panel to close the outflow valve, the emergency ram air inlet, the avionics ventilation inlet and extract valves, and the pack flow control valves.
It seems that it certainly will work on BAT/RAT power only as it is prescribed in the QRH to be used in cases of ENG DUAL FAILURE, such as this case.
Tim