A330 APU BATTERY
My understanding:
The APU Batt only supplies the APU, no exceptions.
In emergency config the APU start is from APU Batt only, the start is limited to F250 max.
In normal ops the APU start is also assisted via the APU TR drawing AC from AC bus 2/external or other engine etc.
Airbus designed the 330 with an APU Batt for:
1. Starts in emergency elec config, preserving the mains for PRIM’s etc.
2. Preserving the main batts for take off.
3. Allowing the quick and easy removal of the batt for cold soak.
4. Can be used as a spare for a failed main Batt.
5. Short wire to APU starter motor = easier to start and avoid hugh batteries for that job.
6. Short wire saves weight.
Waiting for further...