I've said it before and I'll say it again.

If you're so clever, you design a battery pack that'll cater to both the space requirements of a two-seat city car and the power requirements of a 2.5 tonne SUV. Ensure that it's completely future proof as battery technology improves / changes.

Looking at the video, I'd say that that'll have trouble with next year's model of the same car, let alone something a completely different size and shape. $500,000 is a lot to pay for something that effectively comes with the word "obsolescent" stencilled on most of the bits.