The drive to boost mileage is starting a transformation of one of the oldest technologies in autos: the lead-acid battery. The adoption of stop-start systems is helping drive a transition from conventional flooded lead-acid batteries to units that hold liquid electrolytes in absorbent glass mats.
While much of the auto industry’s focus has been on lithium-ion batteries for electrified powertrains, Exide has remained focused on the lead-acid batteries used to start nearly every vehicle on the highways. The company is among the battery makers who are boosting production of absorbed glass mat (AGM) batteries.
The company’s Edge AGM batteries use absorbent materials that hold the electrolytes. Glass fiber mats act like sponges to hold electrolytes. Since liquids aren’t moving around, there’s far less evaporation, so lifetimes can be longer.
“The separator on the old batteries is a piece of polyethylene. In the new technology, we use absorbent glass mats that are a bit like sponges. They are compressible, so everything is held in place. When nothing moves, acid is not sloshing around, which improves lifetimes by a factor of four,” said Paul Cheeseman, Vice President Global Engineering and Research at Exide.
These batteries have seen solid success in Europe, where the popularity of manual transmissions makes it easier to implement stop-start. AGM is gaining acceptance because it can survive far more discharge cycles than the flooded battery technology that has been used for several decades.
“Last year, we shipped 2 to 3 million advanced batteries for stop-start systems,” Cheeseman said. “The batteries last four times longer and the number of times they can start the car is far higher. With stop-start, you’re starting the car 20, 30, 40 times per day or more, depending on traffic. Conventional flooded lead-acid batteries can’t support that many discharge cycles.”
AGM batteries aren’t the only change that is being driven by stop-start. Exide is also moving forward with graphite additives that go into conventional flooded batteries and AGM batteries. Carbon graphite plates shorten recharging times.
“With carbon, it only takes around 20 seconds to recharge after the vehicle shuts down at a stoplight. Without it, it can take over a minute to recharge,” Cheeseman said.
Many observers predict that stop-start technology will see substantial growth over the next few years as automakers struggle to improve mileage. That should spark broader usage of AGM and graphite.
“In the next three to four years, advanced lead-acid batteries should be around 35-40% of the market globally,” said Layna Mendlinger, Exide Senior Director, New Product Development.
She noted that the expansion of electronic controls is also driving OEMs to advanced batteries. They hold a charge longer, which can be a big benefit for owners who leave their cars parked for long periods. Another benefit if that AGMs can be produced in any shape.
“AGM is almost an insurance policy; it lets a lot of complicated accessories run off key for a longer time,” Mendlinger said. “They’re also adaptable. They can be shaped differently, they don’t emit gases, and they can be set on their sides, so they can be placed in the trunk or even under the car seat.”
Though these batteries contain lead, Exide claims they are more environmentally friendly than the batteries that are being touted as the future of electrified powertrains.
“Lithium batteries are more expensive to begin with, and it’s still quite expensive to recycle them,” Cheeseman said. “In the U.S., 90% of lead-acid batteries are recycled, and 90% of the materials can be recycled.”