I wonder what the average power usage is for this target market. I just pulled up my (Tokyo-based, February, 2 person ap't) power bill and it comes out to 670W on average over the month.
People complain about lack of central heating, but I do wonder if that means that in the end lots of space is not being heated.
EDIT: According to [0], Household consumption on average in Japan hovers between 800W and ... 1200W. Of course bigger battery = more time, but 8 hours and 4 hours is definitely qualitatively different.
In Japan, Powerwall is also significantly cheaper than all Japanese maker batteries, last time I checked Powerwall's per-kWh price is only 1/5 of a Panasonic one. How could this happen?
Also Nissan Leaf price (3700kJPY/40kWh, without any grant) is closer to Powerwall (1200kJPY/13.5kWh, without any grant), despite Leaf come with full vehicle feature and V2H. I think Japan home battery market lacks competition.
Power: Toyota: 5.5 kW, Powerwall: 9.6 kW (off-grid).
Energy Storage: Toyota: 8.7 kWh, Powerwall: 13.5 kWh.
If you estimate an average power use of 2kW while off-grid, then the Powerwall gets you 6.7 hours, and the Toyota gets you 4.3 hours of power.