Despite the advancements in lithium-ion chemistry that makes these battery cells smaller, lighter, and more power-dense, the lead-acid box that occasionally strands you before a job interview is not leaving your car. Not even in the 2018 Audi A8, which features a 48-volt electrical system.
Similar to the systems found in the SQ7 TDI, Porsche Panamera, and Bentley Bentayga, the new A8 employs both 12-volt and 48-volt systems connected by a DC-DC inverter, only their operation is essentially reversed in the A8’s application. Here, the 12-volt system is the subsystem; powered by a conventional battery, it runs lighter-load accessories such as the lighting, stereo, and interior power outlets. It’s the primary 48-volt system that gives the car some hybrid functionality.
In principle, a hybrid like the A8 is old news. General Motors has continued refining its setup, called eAssist, since 2006. A secondary high-voltage battery powers a belt-driven motor-generator attached to the engine, which replaces the traditional alternator and acts as a starter when the engine is warm. Honda’s now-defunct Integrated Motor Assist, first seen on the 1999 Insight, put an electric machine in the place of a torque converter. Neither of those systems could propel a car on electricity alone. Instead of a split-power hybrid as in the Toyota Prius, where a traction motor coupled to the transmission can drive the wheels on full electric power or in tandem with a gasoline engine, hyb...