[Charlas]

Can you not get hold of the Audi battery system? Might be the easiest option, mate it to the one the oem uses, and replicate their supply and charge setup.

Seems an interesting project, how much it will however gain you on a 320 is negligible.

 

[Charlas]

M57N2 would be a far better way to spend your money.

Yeah, bigger lump that drops in would be a better idea, but not as much fun from a troubleshooting / solving way.