I am kind of interested in the air batteries, the lithium-air in particular, which has an energy density comparable to gasoline. From what I gather, it might not be unreasonable to imagine a normal-sized battery pack that could provide a 3000 mile range.
There are two major problems with the lithium-air battery. The first is that recharging it in the traditional way just may not be doable. A vehicle might be designed for six 500-mile battery units, which would get used in sequence and theoretically swapped out with reconditioned units as needed (assuming reconditioning is a realistic possibility – if it were, owners might be able to buy reconditioners to keep in the garage, so that they can maintain their own units); for around town, one might be able to save weight by driving around with a partial battery set.
The other problem with air batteries is that they use oxygen. This makes the battery lighter, because it has less stuff in it, but it also means that the battery absorbs oxygen, which means it becomes heavier as it discharges. As ICEs get low on fuel, they become lighter, and BEVs remain the same weight all the time. The idea of a vehicle getting heavier as it runs lower on stored energy is rather counter to what we are used to: remaining range would drop off at a greater rate, rather a lesser rate.
What I could see is a hundred-mile air-battery backup pack, so that one would have a cushion against running the regular battery pack flat.