During an interview with a group of American media this afternoon in Nagoya, Japan, Toyota president Akio Toyoda revealed that his company is already in the process of building a prototype electric vehicle with a Tesla battery pack. The statement came in response to questions about the relationship between Toyota and Tesla. As time ran out, we did not have an opportunity for further follow-up or clarification.
However, both Toyoda and executive vice president Shinichi Sasaki both indicated that Toyota was interested in comparing Tesla's battery configuration against their own internally developed battery. Toyota has a joint-venture with Panasonic that is building larger format automotive batteries that are similar to those used by most other manufacturers. By comparison, Tesla uses commodity 18650-format cells that are typically found in laptop computers. The Roadster's pack contains 6,831 such cells.
The long-term durability of the Tesla approach is still very much in question as few Roadsters have accumulated high mileage – especially in harsh conditions that more mainstream cars would experience. We may or may not ever see a Toyota car with a Tesla battery pack publicly, as it all depends on the results of this study.