A plug-in electric vehicle (PEV) is any road vehicle that can be recharged from an external source of electricity, such as wall sockets, and the electricity stored in the rechargeable battery packs drives or contributes to drive the wheels. PEV is a subset of electric vehicles that includes all-electric, or battery electric vehicles (BEVs), and plug-in hybrid vehicles (PHEVs). In China, plug-in electric vehicles are classified as new energy vehicles (NEVs). Sales of the first mass-production plug-in cars by major carmakers began in late December 2010, with the introduction of the all-electric Nissan Leaf and the plug-in hybrid Chevrolet Volt.