Inefficiencies and durability questions cropping up with now-proliferating stop/start systems could be opening the door for long-promising, but little applied ultracapacitor technology in the light-vehicle market.

Ultracaps, long considered too costly for widespread employment in light vehicles, appear to be gaining traction – albeit ever so slowly – as electrification takes hold and automakers find the technology’s advantages harder to resist, leading supplier Maxwell Technologies contends.

Mikael Setterberg, manager and lead engineer-Engine Starting Group for the San Diego-based supplier, says disappointing battery performance and durability in burgeoning stop/start applications, including with more-sophisticated, advanced-glass-mat (AGM) lead-acid batteries, is leading automakers to take a closer look at UCs.

“You have to change an AGM every 1.5 to two years,” Setterberg says, suggesting an ultracap paired with a lower-cost conventional lead-acid battery can last 10 years/100,000 miles (162,000 km) in stop/start applications.

Even the Advanced Lead-Acid Battery Consortium, which has been solidly behind the AGM movement, is acknowledging a potential future built around a combination conventional battery and ultracapacitor. Its website touts development of the “Ultrabattery,” which would incorporate a carbon supercapacitor electrode to extend battery life and challenge the performance of more expensive nickel-metal-hydride and lithium-ion batteries.

Setterberg points to German supplier Continental’s ultracap-equipped advanced stop/start that is used in a number of PSA Peugeot Citroen cars in Europe as a sign of an emerging trend. The addition of the capacitor allows for a 30% reduction in the size of the vehicle’s battery, Continental says.

Dubbed e-HDi by the French automaker, the microhybrid powertrain is offered in more than a dozen models, with cumulative sales estimated at more than 1 million units.