Did you actually RTFA? The author specifically talked about 12V DC power being the "low voltage" standard that we need to convert to in the home because it's the native battery voltage.
But it's not. It's not the native voltage of any battery chemistry. Lead-acid cells are native 2.0VDC. Lithium cells are native 3.0VDC. Carbon-zinc is native 1.5VDC. Nickel-cadmium is native 1.2VDC. Nickel-hydride is native 1.2VDC. Zinc-air is native 1.5VDC.
All double digit voltages are an artifact of series connection of cells, and the author missed one crucial fact when invoking the Powerwall product: native cell voltage of lithium ion is 3.0VDC, but the Powerwall puts out 400VDC. It is a high voltage product.