I believe its approximately 45 minutes of standby battery power. thats what we learnt on course. I would have to say that QANTAS would have to be the most blessed airline in the world. The tech log shows that the cathay engineers only replaced G.C.U. 2, G.C.U 3 AND B.C.U 1.. i thought that they would of had to replace all G.C.U's, but then a again im only a greaser