Hi Citation2.
In our FCOM this note for the particular fault only appears for recent MSNs (5318, 5592-6267).
The level 2 note says
FUEL CONSUMPT INCRSD
This message is triggered when the failure (or combination of failures) affects the nominal aerodynamic characteristics of the aircraft.
FMS PRED UNRELIABLE
Disregard FMS fuel predictions and refer to QRH/PER-B Fuel Penalty Factors Tables in order to find the applicable Fuel Penalty Factor.
I guess that means you have to check through your sys pages on ECAM and ascertain which bits have been affected (spoilers/ailerons etc) and then apply the relevant factor from the tables in the QRH. As you say, even for one of the MSNs mentioned I cannot find a penalty referenced back to the Bat Fault.
Best of luck.