A few things here...
1. (1) powerwall does not provide very much backup, in most cases. Certainly not enough if one is talking about needing power because of a medical condition.
2. If you are trying to get one "for free" under the equity and resiliency program, that program is pretty much out of money. You can try 3rd party installers to see if anyone can get one for you, but that ship has pretty much sailed, unless more funding is given.
Even if you could get "one or more" powerwalls under this program (if funding is restored) you are likely looking at an install time measured in "many months". If there is an actual need because of needing guaranteed power due to medical equipment, etc, "many months" would not appear to be a reasonable time frame (and that is assuming best case scenario of funding being restored to the program, which I doubt).
Given both of those above, for backup power, you likely want to be looking at a generator, or perhaps a generator while you either work with a third party installer to get one or more powerwalls on your cost, or waiting for funding if you are looking to get one under that SGIP program which is basically out of money.
