A330 FCOM 1.24.10 p4:
"Two main batteries, each with a normal capacity of 37 ampere-hours, are permanently connected to the two hot buses.
A third battery (37Ah) is dedicated to APU start."
I'm not sure if this an answer to your question, sequence:
APU batt => APU start => APU AC generation => Main batts charging via AC bus, TR and DC bus
APU batt for APU only (in normal operation). Check your FCOM1 in Electrical and APU, you should find all the answers.
Regards.
Last edited by barrel; 21st July 2012 at 13:15.