There are about $4K worth of batteries in a tesla, at approx. $0.50 per cell.
Tesla has been using 18650 cells manufactured by Panasonic in Asia in the Models S and X cars since 2013. These are small battery cells, slightly larger than the standard AA cells. The Tesla cylindrical cells are 18 mm in diameter and 65 mm tall. The Panasonic design, perhaps with input from Tesla, is by some accounts one of the most robust formulations available today, yielding very long-lived, reliable performance in the harsh automotive environment.
Above: Panasonic's 18650 battery cells used in the Tesla Model S and X (Image: PBS)
The most popular battery pack supplied by Tesla contains 7,104 18650 cells in 16 444 cell modules capable of storing up to 85 kWh of energy. In 2015 Panasonic altered the anode design, increasing cell capacity by about 6%, enabling the battery packs to store up to 90 kWh of energy. More recently, Tesla engineers reconfigured the internals of the battery pack to hold 516 cells in each module for a total of 8,256 cells capable of storing a little more than 100 kWh of energy enabling the cars to enjoy a range of over 300 miles.
https://evannex.com/blogs/news/understanding-teslas-lithium-ion-batteries