Audi's battery acquisition plans and potential are IMO unknown, we don't know enough, so it comes down to what we believe. Mind you, I'm not saying batteries are not an issue especially for the 2018 model, but I do believe there is a serious plan and capability to execute a ramp-up for Audi that starts in 2018.
Based on what?
VW Group thought about establishing their own battery plant in Germany back in May/June/July last year:
VW mulls $11 billion battery cell plant
Hmm... right when the Model 3 reveal hoopla was going on... The Salzgitter plant was even reported as decided by several media outlets.
Then by September:
Volkswagen CEO denies plans for EV battery plant
Now Volkswagen CEO Matthias Müller qualified these reports as “complete nonsense”. In an interview with business paper Handelsblatt, Müller said “we certainly won’t do such a nonsense”, referring to the reporter’s question if the company had any plans to fabricate their own traction batteries.
The idea that they can just source their batteries from LG and Samsung is laughable if they were really aggressively cutting over in the 2019 through 2022 time period. For example, Samsung SDI's Hungary plant is a meager one... only $358 million invested, starting operations in 2H 2018 for roughly 2 GWh. It will take 2 years just to start operations for this small-ish plant. LG Chem's Poland plant is likely going to be twice the size, going to maybe 3 times eventually. The two added together, with 2019-2020 capacity, is less than Tesla's 2017 capacity for the Gigafactory 1. That's to supply Volvo, Renault, VW, Audi, Porsche, Nissan, and others. The Chinese capacity likely goes towards Chinese demand, the LG plant in Michigan is making cells for the GM/Ford/FCA at a mere 2-3 GWh, and SK Innovations is only going to 4 GWh for Mercedes. It takes years to bring capacity online... for 2019, it's already late for multi-GWh factories. Likely a project starting today for 10+ GWh will not be online until the 2020's.
More on VW's lack of vision:
Is the industry zooming toward a battery shortage?
The reality is that the major automakers will likely wait for solid state chemistry to overcome its big hurdles before committing heavily to BEVs. In the meantime, they'll make all sorts of FUD to try to rein in Tesla as they play this waiting game. They hope that the chemistry will be viable in the 2020's... and then they don't have to worry about the current generation of BEVs. So they make a few token ones to satisfy governmental regulations and what they perceive as the token small market.