You actually don’t need a power grid to generate electricity, just a water wheel or some solar panels. I’ve been to some off grid places in China that mostly use water wheels, crazy stuff. Many Alaskan communities aren’t connected by grid to the outside but have local hydro stations to supply all their needs, with maybe diesel as a back up. Hawaiian islands are similar, but with solar instead of hydro.

If the apocalypse comes, EVs will be running for a lot longer than ICEs.