Not to defend Tesla in particular but rather to question people's expectations... I think that people have to stop branding the Powerwall battery a failure because it can't power all of a household's high wattage appliances at the same time.
If you're already off-grid, then you're probably already well aware that electricity usage has to be somewhat planned and you can't just wake up in the morning and fire up the toaster, kettle, oven, electric shower, hairdryer, curlers, washing machine and dishwasher simultaneously and to suggest that this battery, which is probably smaller and less robust than a lot of true off-grid'ers battery banks, should be able to do that seems rather unfair.
It's most valuable achievement seems to be raising awareness of the need for energy storage in a green energy dominated grid. Whether it's a good product seems rather less certain from the specs. I thought lithium cells were supposed to avoid the lead acid pitfalls of limited charge cycles and death by excessive discharge etc? Apparently not these...
Perhaps a more natural market for these sorts of mass-market, plug-and-play, all-in-one, certified and standardised solutions will develop as an integral part of a smart grid, controlled by the National Grid who would govern when and what wattage the Powerwalls would release to homeowners:- With the Grid sending out automated messages like "Calling all Powerwalls... calling all Powerwalls... calling all Powerwalls: The Greens haven't touched their lentil and bean soup today and so mighty fleets of wind turbines aren't quite spinning fast enough to generate enough electricity to meet demand. Can you all switch on and each reduce your house's draw from the grid by 500W using the energy you were able to store from your solar panels earlier when the sun was still shining out of the Greens' arses"