You may wish to look at
http://www.pprune.org/tech-log/48026...p-apu-ops.html.
for extended APU ops should all fuel pumps be turned on or should only one of the left wing tanks be turned on?
as per Boeing, yes, one of the left, centre with fuel, or right with crossfeed.
I ask because I have observed that a small imbalance develops between the port and starboard wing tanks when one wing tank pump is turned on.
- most unlikely, and if it is the APU causing the 'imbalance' (40kg per hour - you must have very good eyesight!!) then it happens pumps on or off.
. So I basically want to know if it's okay to turn on all fuel pumps once battery dependent electrical power is established.
- no reason why not but they will not run as they are AC. However, since it is generally my policy to be kind to aeroplanes (with a few exceptions....) I would leave them off so when you put generator power on there is no surge of demand