This is where it matters most in hybrid cars. The Prius Prime features a 1.8 L, Atkinson-cycle mill similar to the one on the outgoing Prius. The engine has been upgraded to achieve a 40% thermal efficiency. The other half of the drive-train features a new 8.8 kWh lithium-ion battery pack which is paired with a dual-motor drive which uses a one-way clutch to engage the electric motor and the gasoline engine. All the juice is sent to the front wheels via a planetary-type CVT system.