Capacitor-based regenerative braking

Robust and lower cost "mild-hybrid" technology.

Unlike batteries, capacitors can charge quickly and discharge rapidly when needed; and, unlike batteries, they don't deteriorate in prolonged use.
Mazda's brake energy regeneration system (i-ELOOP) is unique because it uses a capacitor instead of battery.
'i-ELOOP' efficiently converts the vehicle's kinetic energy into electricity as it decelerates, and uses the electricity to power the climate control, audio system and numerous other electrical components. 
While the gasoline version of the 2014 Mazda6 earns 26 mpg city, 38 highway in the EPA cycle, the i-ELOOP version earns 2 mpg better in both the city and highway cycles.

CSM: 2014 Mazda6: Impressive mileage, sporty package