Are they using significantly different technologies for the individual cells? I always found it weird that the large battery in a Tesla, for example, was just made up of thousands of 18650 cells that are probably smaller than the battery in your phone. Is the Powerwall is the same?

Does it get any different at larger sizes? Obviously stuff must be different outside of the cells, even if the cells are the same.

Of course this is also why I think there are some cost reductions on the horizon, as current EV and grid tied batteries are basically just a bunch of laptop batteries thrown into a fancy box.

I also read something like that. I suspect it is more of a tweak than anything major. No doubt it is the same basic chemistry but perhaps with minor tweaks to the various ratios and material thicknesses and so on. The Tesla batteries are a single-application cell, so you know exactly the maximum discharge current, the maximum charge current, the temperature parameters, and so on, whereas a generic 18650 has to balance those for a "typical application" or whatever. See for example the Samsung high-discharge INR18650 cells which trade off capacity for higher max discharge current.

OTOH the other hand I also heard the early Teslas were using exactly the Panasonic 18650B cell. They could both be true: maybe it was a stock cell in the early days and they tweaked the formula later in concert with Panasonic as their volumes rose. There was no big evident spike in capacity vs weight though...