DIY Powerwalls aside, the idea of procuring cells across various "dead" batteries is amazing for the environment. A lot of times, people just throw out the entire battery even though only 1 or 2 cell is dead which shuts off the entire thing. But this is literally the 2nd-R in "Reduce, Reuse, Recycle", which comes before recycle. I know there's a notion that recycle makes everything so much cleaner but there's a reason why its the 3rd-R in the motto.