The assumption is apparently[0] 30 kWh/day counting as "full usage," giving 3 days of runtime. Rationing that can give you up to 10 days, implying 9 kWh/day.

I have a full electric house in central Texas, and my daily usage in the summer is around 2000 kWh, so I could get about 1.5 days of power if I did nothing to ration it. If you have a gas water heater, stove, dryer, etc. it'll obviously stretch out.

[0] https://www.thedrive.com/tech/40695/the-electric-ford-f-150-...

EDIT: s/daily/monthly