Power walls are expensive. You may be better off looking at a NG generator and then doing an on-site reserve tank that feeds off the utility line. That could keep you online for weeks if it’s designed right and if you’re savvy, the cost for this could be about the same as a powerwall.
That’s kinda how a friend of mine built his house here in CO. It’s solar as well, and typically generates enough power in a day to recharge his 2 x power walls 1.5x. He then has an NG generator that’s linked to an underground tank that fills off the utility line.
Pretty smart. House basically takes care of itself and in the event it doesn’t (say during a week or two long snow storm), the generator is there. And if the utility kicks off, the tank can feed the generator for more than a month. More than enough time for any weather to clear and sufficient solar to kick back in.
I think in your case, since you don’t have solar, just the same idea around the generator + tank could work well without breaking the bank too much?