Good stuff to see how you can just take those packs apart and recombine them, but aren't you supposed to take care to match cells and make sure your BMS can balance the charging or risk letting the explosive magic smoke out? Seems like he just took any random cells and put them all together.
He didn't really talk about any of that, so this approach feels like quite the fire hazard.
DIY super capacity BATTERY PACK
https://www.youtube.com/watch?v=qZ_dwesKFwY