The problem until recently was that gas generators are, in many places, banned. Apartments are a no go, many condos, and even some house HOAs do not allow them.

Now, lithium backup packs are a thing. However, for any extended needs you will probably also want solar panels or some other way to recharge, and you may need a second battery so that you can recharge one while using the other (the units I purchased do not allow discharge while charging)