While the design of most major automotive systems is pretty much a known quantity, the battery pack required some real innovation to ensure reliability and safety in addition to performance. After at least seven major design iterations of their pack system, Tesla has now successfully done a 50mph rear end crash test of the roadster.
Having reached this point Tesla has created the Tesla Energy Group to offer their pack technology to other manufacturers. Their first customer will be the re-born TH!NK. TH!NK is the Norwegian electric car builder formerly owned by Ford and they're working to bring a new design car that was designed during the Ford era to market. Other manufacturers have expressed interest and hopefully the increased volumes will help drive down the cost and drive up the rate of development.
[Source: Tesla Motors]