One of the ways hybrids achieve big efficiency gains is through something called a start-stop system: When a Prius rolls to a halt, so does its engine, saving fuel and boosting miles per gallon. The car’s advanced battery keeps the lights on and the stereo buzzing until the pedal is pressed and the engine restarts.
In the U.S. that kind of efficiency gain hasn’t been available in regular cars because their lead-acid batteries would go dead in months if they had to restart the car so often. But new federal efficiency standards are encouraging automakers to wring every mile out of a gallon of gas, and a battery design from Johnson Controls, the Milwaukee-based industrial giant that makes a third of all auto batteries, will help. The company is currently retrofitting a factory west of Toledo to begin making its advanced batteries, which will power start-stop systems in conventional autos beginning next summer.
The efficiency gain is modest, improving mileage by about 5 percent, but will save a sedan-driving family about $100 a year in gas costs and could have a large aggregate impact. It’s a tweak that will help the auto industry meet a new mandate by President Barack Obama to improve its corporate average fuel efficiency by 100 percent, to 54.5 mpg, by 2025. “It’s not a wholesale change. It lets the automakers build on what they’re already good at,” says Craig Rigby, Johnson Controls’ head of product engineering. “That’s what I think is the beauty of start-stop.”
Johnson Controls’ advanced batteries employ a technology that was first used in the 1980s for fighter jets. A typical car battery uses a gallon of acid and water as an electrolyte, which enables the electrical charge to flow but also eats away at the battery’s innards. In the advanced battery, the electrolyte is stored in an absorbent glass mat, which has the look and feel of a strong paper towel. It serves as a pathway for the electrical charge and limits the exposure of important components to the corrosive electrolyte, thus prolonging the battery’s life.
Stop-start systems, which include not just the battery but brake sensors and other custom car parts, should add about $500 to the purchase price of a new car, according to Johnson Controls. They’ve been used in conventional cars in Europe, where gas can cost more than $8 a gallon, for about five years. Mike Wall, an analyst for IHS Automotive, estimates stop-start systems will be installed on about 20 percent of new vehicles in North America by 2017, up from about 2 percent now. “This is sort of a bridge that will help us get from here” to an all-electric future, Wall says. Ford Motor plans to start selling vehicles with start-stop systems next summer, although it declined to specify the exact models and prices.
The efficiency push is good news for Johnson Controls: The advanced batteries are twice as expensive and three times as profitable as traditional ones, according to the company.