VW just made clear that they have no competence in batteries and even decided to lower spending in Development so they don't intend to build that competence in difference for instance to BMW. Tesla has likely the largest Battery development center in house globally testing and investing in every aspect and continue to find ways and technology to make the next improvement work.
So, yes on paper it looks like both outsource to Batterie producers but looking into details you realize that Tesla is the driving force in designing the Batterie technology as well as keeping the Batterie pack production in house.
IOW there is a large difference in how Tesla and VW approach the technology development and innovation. VW does consider the Batterie technology as not strategic and not as a IP they need to own as they do with the ICE drive train. Since years German automakers are stating that the Batterie technology is for every producer globally the same which is just not the reality.
If it is like that what they claim why haven't I see yet a VW EV with low price and range of 500km yet?
Just imagine a large European ICE producer is telling you the drive train of the vehicle is not their core competence and the will supply them from Asia. What kind of car would you expect from them?
"Development spending
Even with its push to ramp up electric-car production and avoid penalties from tighter environmental regulations, Volkswagen plans to rein in expenditures. Development spending declined 3.9% to about $16 billion in 2017, equivalent to 6.7% of sales. The company reiterated a
target to lower that to 6% by 2020."
Volkswagen pours $25 billion into electric-car batteries, challenging Tesla
"Manufacturing the powerpacks themselves is not in the cards. “
This is not one of our core competencies,” said Mueller, who has faced pressure from employee representatives to invest in battery-cell production. “Others can do it better than we can.”"