Batteries are still expensive, and wear out. We are realistically not going to replace ICE engines in substantially less time then 20 years, probably closer to

Batteries are still expensive, and wear out. We are realistically not going to replace ICE engines in substantially less time then 20 years, probably closer to 50 or 100 even given penetration. What we can do is replace the origin of their fuel source, and the cheaper the better. You can synthesize methane into any liquid fuel you like. Now you'll lose energy in the transformation, but if the input energy is cheap and abundant enough - and can be stored well enough - then maybe that doesn't actually matter. There are large areas of the planet which get more then enough sun to provide all our power needs and would impact no one if we harvested there. But we can't get the energy out of them, and we can't store enough of it to cover the times we can't.