Tesla uses Panasonic cells to make their batteries[1]. I'm sure Tesla has some circuitry/electronics to control the cells, but it's not like the key battery technology is all Tesla's.

The Gig Factory allows Tesla to ensure they have enough batteries for their car fleet so that they don't suffer from shortages as other MFGs put a demand on suppliers.

[1]http://www.greencarreports.com/news/1104609_panasonic-to-bui...