&gt;But the Prius combines both technologies and gets 40% thermal efficiency<p>well, you can get an even better ICE with relatively simple improvements. In some sense there is just no business case for it as metal-air batteries would probably beat all the other options for passenger cars in near future.<p>&gt;Many think that hybrids and plug-in hybrids are a bridge technology to a pure EV future. But the future may end up being a lot more similar to the present than expected. Maybe the typical car purchase in the future will be a 100 mpg hybrid with 60 mile plug-in battery range as an option.<p>kind of. Small personal cars will go EV (typical secondary and metal-air batteries). Starting with pickup trucks and into the big ones - will be hybrids with various plugin (probably with metal-air or similar) options.