OK here are some more thoughts:
The APU Batt is only for the APU, at all times.
In normal ops the APU start is also assisted via the APU TR drawing AC from AC bus 2/external or other engine etc.
In emergency config the APU start is from APU Batt only, the start is limited to F250 max.
So all this is great in terms of how it works. Thanks for the help.
But still, did Airbus design the 330 with an APU Batt for
1. Starts in emergency elec config.
2. Preserving the main batts for take off.
3. Allowing the removal of the batt for cold soak.
4. Combination of the above.
5. Other?