That does not work. A Powerwall or other battery will just increase the base load over the time it's charging (or decrease the load when it empties), but you will still have noticeable load spikes by which you can identify the device.

Actually, it's even possible to identify certain devices by eye if you have a sufficiently detailed log (I could, for example, distinguish a coffee machine, a dishwasher and a fridge, as well as lights with different wattages, at a resolution of 1-2 measurements/s). Their patterns are quite distinguishable.

Oh, I definitely agree. The cistern analogy with water would function the same way-- refilling from the public water supply as it was drawn upon. I assumed one would disconnect from the public utility input to obscure usage patterns, "refilling" in bulk at a later time. (I did think the Powerwall was aimed at load-shifting, though, too.)

I believe this is how the sense.com devices work...