I see separate paths for mobile vs stationary battery solutions. Stationary need high capacity with lots of cycles and low cost. Mobile need to be light, compact, high capacity and cheap. Eventually the two paths may merge, depending on how the technology develops down the road, but right now lithium/sodium are better suited to stationary instillation, while lithium/polymer might be the preferred route for mobile application. But hey I am just an interested bystander, I might be out in left field for all I know. Fun stuff though!