I guess I was not clear in my previous post. You cannot use a vehicle as a backup power source for your house. The NEC prohibits it. If you try to do this you will not pass inspection. The only way to legally obtain backup power from the R1T would be to run an extension cord out to it and plug that into one of the bed outlets. These are rumored to be able to supply 15 A @ 120 V equal to 1.8 kW. A fully charged 180 kWh battery can supply that much power for 100 hours (4 days and 4 hrs). As mentioned in No. 19 the average Texas house consumes 14 MWh/yr. That works out to an average demand of 1.6 kW. A 13.5 kWh back up battery will, therefore, last, on average, 13.5/1.6 = 8.4 hours unless you institute some sort of load shedding when the utility goes down. Were it legal to draw energy from the vehicle (and were the modifications made to the truck and the EVSE to allow this) a fully charged 180 kW battery would supply an average load of 1.6 kW for, on average, 4 days, 16 hours and 30 minutes. The big difference between the powerwall or the proposed illegal truck hookup is that they will supply the brief peak loads (such as a 6 kw air conditioner cycle) whereas the legal truck hookup is limited to a peak draw of 1.6 kW. Thus a power wall is great for short outages (as many tend to be) but pretty useless when the power goes out for a couple of days unless you impose strict shedding or install multiple power walls. For longer outages you still need a generator.
