Because currents are reduced with 48V, less copper wire is needed, and plenty of power available to run air-conditioning compressors, vacuum pumps and electric superchargers, all features that would be needed for a downsized hybridized powertrain.

Pels says a 48V hybrid version of a 1.2L engine with an electric supercharger could match or beat the performance of a 1.8L Tsi engine while reducing fuel consumption 24%.

AVL worked with the Advanced Lead-Acid Battery Consortium to produce a prototype Volkswagen Passat shown at a powertrain conference in Vienna in April that uses a 48V lead-acid battery. Nick Pascoe, CEO of U.K.-based Controlled Power Technologies, says using the lead-acid battery means the add-on cost to the customer for a mild hybrid would be only €1,150 ($1,500).

Pels says many auto makers limit their 48V planning to Li-ion batteries, “but there is safety, lifetime and quality to be considered.” Lead acid has high specific power of 800-1,000 W/kg, but is weak in specific energy at 35Wh/kg-40 Wh/kg.

“While this is certainly a disadvantage, we believe we can package those batteries and it should not be the sole criteria,” he says. “OEMs should take it seriously. The test results are promising, and it makes sense to further evaluate this technology.” As for hybridizing diesels, “combining expensive electrification with an expensive powertrain is not evident.”

Valeo’s mild-hybrid approach is similar, says engineer Damien Fournigault. In tests integrating its 48V electric supercharger on a 1.6L turbocharged gasoline direct-injection engine, the supplier calculates stop/start cuts consumption 5.5%, braking regeneration and torque assist another 5% and a zero-emissions electric mode an additional 3.4%. Valeo’s first such system will be in production in 2015-2016.

Both Valeo and AVL also are working on connecting GPS and sensor information to the system to predict energy requirements, which will allow a car to better manage its limited electric storage capability.

Knowing the vehicle must slow down for a coming roundabout, for example, Valeo’s “Copilot" could cut off fuel injection and switch to electric power before the driver lifts his foot off the accelerator, because the car will know that the battery will be recharged at the roundabout.

Valeo believes the system could add up to 3% in real-world fuel-savings, although just 1%-2% on the New European Driving Cycle homologation driving cycle.

AVL’s Laurent Allouchery, a veteran of PSA Peugeot Citroen and Renault, estimates adding predictive energy requirements to a car will allow the battery to charge and discharge at the optimal state of charge and will cut fuel consumption 3%-4%.

“It is a cheap way to reduce CO2 emissions and get a better battery lifetime,” he says. “Customers will see the benefit.”

While it’s clear to these engineers that the internal-combustion engine will survive at least through 2030, “the powertrain can’t do it alone,” says Renault’s Doublet. “It needs energy recovery, and it has to be combined with huge reduction of vehicle energy needs. It has to be right-sized accordingly. The zero-emissions vehicle in the city is a must for the long term.”