What I find unreasonable about barring the fuel is the availability of food sources and fresh clean drinking water not to mention the endless supply of ammo that one would assume would have been used up within the first few days, weeks, months of infection let alone a few years.
They probably get the batteries from the same place they keep getting this years new cars. Every time I see one of the new vehicles I think of factories in Korea (Hyundai) filled with zombie workers pumping out new cars.
Another thing that kinda irks me is when they do supply runs, and search through say a house, why are they being so picky about only getting the specific item they are looking for? I would be raiding the cabinets, drawers and closets of any vacant house I would go into searching, taking as much as I could carry, especially when there is a whole group you are trying to support. And the stores, clear the shelves. Take everything you can carry.