Saptzae.
The APU AC BUS can be tied to the L and R AC busses.
From what I can see the only connection from the APU Battery is through the Start Power Unit (SPU) this converts 28vDC to 115vAC this then goes to the ATRU which converts to +/-130vDC which via the CMSC (Common Motor/Start Controller) is routed to the APU starters (VFSG). The APU hot bat bus doesn't connect to anything else from what I can see except if the Towing Switch is selected 'on'. In which case it powers the Position lights.
The APU charger receives it's power from the FO's Instrument Bus.
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