Thinking a little more about it, I don't think it would be good for our current eink displays to add an other thickness. They already suffer from a lack of contrast due to the concept itself of the 'grids' that orient the colo(u)red particles. Adding an other layer over would further the loss of transparency however transparent this battery system may be. Do a test with ordinary glass, just pile panels atop one an other and compare light coming through. Plastics are even worse.
But they would work wonders on backlit displays.
