"Standby power from the batteries provides electrical power to the standby compass/standby attitude director/standby ASI, for a minimum of 30 minutes."
An almost full list can be found on the D&G forum. The pilots were certainly not relying on tiny clockwork instruments under Standby Power. The Captain would have had all his glass instruments running and would also have had the Left FMC and Left MCDU at his disposal. The Upper EICAS would also be working (I imagine with all engine parameters available in a compressed format). However, I praise them for keeping their cool.
I don't have details handy for the ISFD's fitted to QF's 747-400ER's, but I believe it is more towards 3 hours of battery life (and provides attitude information as well as airspeed and altitude. The airplane in BKK was not this type however.
Rgds.
NSEU