One thing that often strikes me is the use of 18650 cells in an unpractical, though technically and economically correct way. Even low power laptops today employ series of multiple 18650 cells in parallel, so why not make an effort to bring down the price of bigger cells such as the 26650 or 32650? today the 32650 costs more than the sum of the 18650 cells it replaces, which clearly explains the wide use of 18650s, but using that one would also reduce the number of cells by 2 or 3x, therefore saving some good money in both time and parts (wires, fuses/protections, holders etc). I'm talking about generic lithium cell production and marketing, not this project which is truly great even just for avoiding the burial of used cells in some 3rd world landfill.