If you think a plug-in diesel hybrid is an expensive proposition, just wait until you hear details about the just-revealed Audi A7 Sportback H-Tron Quattro. The "H" in H-Tron, as you might guess, stands for hydrogen, so say hello to a new concept that combines a plug-in battery system with a hydrogen fuel cell. On the plug-in side, the new H-Tron has an 8.8-kWh lithium-ion battery that can power the car for up to 31 miles on battery power. With electric motors on both axles – it's a Quattro, after all, but a through-the-road hybrid with electronic torque distribution management – the A7 H-Tron uses a hydrogen fuel cell and four (!) H2 tanks to offer about 62 miles per gallon equivalent. Audi says the overall fuel cell stack efficiency is "as high as 60 percent" while the electric motors operate at 95 percent efficiency.
