The main issue with using a large EV battery pack as temporary home back-up power is the liability around "back feeding" the grid, if your homes electrical system is still connected to the city grid.
If you have solar panels and a large home battery, most people have a "grid connected" system, instead of free-standing (I am a fan of free standing). The main feature of a grid-connected system is a switch that meets all the performance and safety requirements. This means when the power from the city goes down during a storm, the switch automatically cuts off your home from the city-grid, and powers your home only from your home back-up battery pack. It will have to be "re-set" when the city power comes back online...
The safety fear is that...if a power line is down on the ground during a storm, and a utility worker is trying to fix it, they will have tested it for current, and with a zero reading, they will proceed with the repair. Then suddenly, you power-up your home by flipping some UN-authorized switch, which not only powers up your home, it sends power down the outdoor lines that are in the process of being repaired, and may electrocute someone who is standing near a power cable that is laying on the wet ground.
There is a large simple switch in a fusebox that connects the city power grid to your home. Rather than fiddle with that, I prefer to run an extension cord from an inverter that is connected to my ebike batteries. In an emergency, I will not be running my air conditioning. I only need to power my refrigerator, a few low-watt lights, and my TV plus laptop computer.