During a 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.