Is Stop-start Idle Elimination Crushing Vehicle Electrification?

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John Petersen

Since June of 2009 I’ve been a voice in the wilderness proclaiming that stop-start idle elimination will become a dominant automotive fuel efficiency technology by mid-decade and represent a tremendous business opportunity for established lead-acid battery manufacturers like Johnson Controls (JCI) and Exide Technologies (XIDE) and emerging energy storage technology developers like Maxwell Technologies (MXWL), Axion Power International (AXPW.OB) and A123 Systems (AONE). In the process I’ve suffered more than a little abuse, scorn, derision and ridicule from EVangelicals who think it makes sense to propel up to 5,300 pounds of metal at highway speeds with quarter-ton battery packs. With each passing day, however, it becomes increasingly clear that my cautious assessment of electric drive and my optimistic outlook for cheap and simple fuel efficiency is spot-on accurate because, in the words of Vinod Khosla, “Economics matter and nothing that defies the law of economic gravity can scale.”

The most recent confirmation that stop-start will leave all other vehicle electrification technologies in the dust over the next decade comes from a Pike Research report titled “Stop-Start Vehicles, Micro Hybrid Technologies, Batteries and Ultracapacitors; Market Analysis and Forecasts,” which reports that while stop-start technology is not well known or understood in North America, stop-start vehicles, or SSVs, are already outselling hybrids by a factor of 3.5 to 1 and the stop-start advantage is expected to widen to 16 to 1 over the next few years because of low cost and easy integration.

11.1.11 Pike Graph.png

In its discussion of the business opportunity Pike said, “Global revenue from the sales of stop-start batteries will grow from $827 million in 2011 to $8.9 billion in 2020, at a compound annual growth rate of 30%.” The Pike report mirrors similar conclusions from Lux Research in their October 2010, report “Micro-hybrids: On the Road to Hybrid Vehicle Dominance.” Both reports are a good deal more conservative than EPA forecasts that stop-start will be implemented in 42% of US light duty vehicles by 2016. In a weirdly ironic Halloween twist, Wunderlich Securities analyst Theodore O’Neill blamed the rapid adoption of stop-start for limiting demand for lithium-ion batteries and plug-in vehicles. “Where it went off the rails,” said O’Neill, “is all the major car companies figured out in 2009 that they could use a different technology to meet the emissions standards in the U.S. and in Europe … That technology is start-stop.”

I’ve always argued lead-acid batteries would remain competitive for decades as the battery of choice for cars with internal combustion engines, but I never expected to read that stop-start technology and lead-acid batteries were crushing vehicle electrification. Score one for the home team!

Even though stop-start has had a hard time catching the mainstream media’s attention, it’s the most sensible and cost-effective fuel efficiency and pollution reduction technology imaginable. It automatically turns off the engine when your car isn’t moving and instantly restarts the engine when you take your foot off the brake. The biggest problem with stop-start is that it’s a battery killer because instead of starting the engine once when you begin a trip, it has to start the engine several times during the trip, carry accessory loads during engine off intervals and recover its charge very quickly to prepare for the next engine off opportunity.

The conventional flooded lead-acid batteries that we’ve all come to know and hate are simply not robust enough for stop-start. So the auto industry needs a better energy storage solution to accomplish the worthy goal of eliminating wasted fuel and useless pollution from idling vehicles.

The auto industry’s widespread and rapid adoption of stop-start has come as a big surprise to most battery manufacturers and industry analysts. Historically almost all cars used flooded lead-acid batteries for starting, lighting and ignition. While AGM batteries have existed since the 70s, global production capacity was limited to a few million batteries a year and most AGM batteries were used in aviation, marine and other high-end applications where their sealed design avoided problems with electrolyte leakage, gas generation and maintenance. Simply put, the world’s battery manufacturers were not ready for a surge in AGM battery demand from the auto industry which needs about 55 million batteries a year.

Since the world’s battery manufacturers didn’t have enough factory capacity to make AGM batteries for the auto industry, their first response was to introduce enhanced flooded batteries that don’t perform as well as AGM, but can be made in existing plants. Their next response was to go on a huge capital-spending spree to build new AGM battery manufacturing facilities. Between 2002 and 2009, JCI averaged about a million AGM batteries per year. By 2015 it plans to make about 18 million AGM batteries a year. Exide is also expanding its AGM capacity from 500,000 batteries a year in 2010 to 5.5 million batteries a year by 2015. Other battery manufacturers are quickly following suit.

When Citroën and BMW introduced the first stop-start systems in 2006 and 2008, the technology was viewed as a modest advance with an uncertain future. The initial reviews were less than flattering because the systems performed fabulously in new cars but suffered sharp performance declines as the batteries aged. That gave rise to a concerted industry-wide effort to learn why lead-acid batteries failed in stop-start vehicles and find solutions to the problem.

At the 2010 European Lead Battery Conference, BMW and Ford explained the problem of dynamic charge acceptance to the world’s lead-acid battery manufacturers and used the following graphs to show how AGM batteries used in stop-start systems begin to lose their dynamic charge acceptance almost immediately and become effectively worthless after a few months. They also explained that unlike traditional vehicle designs, engine starting was only a minor issue in stop-start because over 90% of the energy used during an engine off interval was attributable to accessories, rather than the starter.

11.1.11 BMW Ford Graph.png

While the graphs provide a lot of data the most important line has a burgundy highlight and shows how charge recovery time increases from 30 seconds with a new battery to several minutes with a battery that’s been used for a few months. Since stop-start systems disable themselves until the battery has recovered, a battery that can recover in 30 seconds will invariably sav
e more fuel than a battery that needs several minutes to recover.

Today the auto industry and the battery industry find themselves at an impasse over battery performance in stop-start. The automakers have made it clear that traditional AGM technology is not good enough for today’s stop-start systems and can’t possibly support future stop-start systems that will offer better fuel economy and put even greater strain on their batteries. The battery industry has responded by producing enhanced AGM batteries that are an improvement over traditional AGM technology, but remain inadequate for the demands of future stop-start systems. To solve the problems and accomplish their fuel economy and emissions reduction goals, most automakers are actively evaluating other technology alternatives.

Continental AG and Maxwell Technologies developed the first new approach to energy storage for stop-start. Their system combines a supercapacitor module with an AGM battery to ensure that stop-start diesels from Peugeot Citroën have enough cranking power to reliably restart the engine. In their second quarter conference call, Maxwell’s CEO noted that the system would also increase AGM battery life by roughly 30%. While the Continental-Maxwell system can’t do much to overcome the dynamic charge acceptance limitations of AGM batteries, Pike believes supercapacitors will be used to complement batteries in stop-start systems for diesel engines.

Axion Power International is presently completing the development of a second novel approach to energy storage for stop-start and preparing to launch their first product. Axion’s PbC battery is a hybrid device that replaces the lead-based negative electrodes in an AGM battery with carbon electrode assemblies that eliminate sulfation, the chemical process that causes conventional AGM batteries to lose their charge dynamic acceptance capacity over time. Since the PbC is a third-generation lead-acid device, it can be assembled on any conventional AGM battery line. In over two years of exhaustive testing by BMW and others the PbC has demonstrated remarkably stable dynamic charge acceptance through several years of simulated use in a stop-start vehicle. While the PbC is not currently available for use in stop-start vehicles, the Pike report suggests that the PbC will be available for use in 2013 model year vehicles.

A123 Systems has recently announced the launch of a lithium-ion battery for stop-start vehicles. Their engine start battery combines sixteen of their 20 Amp hour cells with associated control electronics to deliver a kilowatt-hour of energy and the cold cranking amperage necessary for an automotive starter battery. Because of the high cost of lithium-ion batteries, Pike believes their market penetration will be “very limited” and restricted to expensive performance vehicles.

Stop-start presents a rare dynamic for the lead-acid battery industry because the new technology solutions from Maxwell and Axion will complement rather than compete with existing battery products. Supercapacitors from Maxwell will function as add-on component that improves the efficiency of today’s AGM batteries. Similarly, carbon electrode assemblies from Axion have been designed for easy integration into existing AGM plants as a plug-and-play component that can make today’s AGM batteries better. Both technologies can help established battery manufacturers better serve their customers needs without eating into their revenue from product sales. For both companies, the ability to leverage existing manufacturing facilities, distribution networks and customer relationships should facilitate a much faster ramp rate than one could expect from a new product that needs to overcome entrenched competitors, build manufacturing, distribution and customer service capabilities and divert staff from other lucrative markets.

JCI and Exide will be the first big beneficiaries of the global shift to stop start. Both companies are trading well off their historic highs and have attractive upside potential. As products from Maxwell and Axion prove their merit in stop-start vehicles and increase production capacity, their shares should perform well. Since Axion has a market capitalization of $40 million while Maxwell is valued $550 million, Axion has greater upside potential for risk tolerant investors.

Currently, the media hype is all about lithium-ion batteries and plug-in electric drive, but auto industry’s production plans are all about stop-start and other fuel efficiency technologies. Given a choice between chasing sunshine, lollipops and rainbows or investing in an established automotive trend, I’ll take the established trend any day.

Disclosure: Author is a former director of Axion Power International (AXPW.OB) and holds a substantial long position in its common stock.


  1. I think you may be a little quick to dismiss Lithium-ion’s potential in stop-start. I think you’ve made a good case that only PbC and Li-ion have the durability needed for this application. Also, from other articles you’ve written, I gather that you expect a PbC battery to cost about $250, while a Li-ion battery will cost about $1000 for this application (correct me if I’m wrong.)
    The $750 cost advantage for PbC seems compelling except when you consider that 1) Li-ion is a much better understood technology, and 2) the weight advantage.
    Weight is very important in vehicles, and if the Li-ion battery can save 50-100 lbs, that has the potential to, in itself, improve fuel economy. I’m not sure how much it will improve fuel economy, but it should be enough to be worth some premium to automakers.
    Obviously, my numbers need to be checked, but that might be a good subject for your next article.

  2. The lithium weight advantage is on the order of 25 pounds, which is pretty meaningless in the context of a car. While the chemistry is well understood by the automakers, it’s not well liked.
    Besides, it wasn’t me that dismissed lithium as a bit player. The exact quote from Pike’s executive summary says:
    “The market will be dominated by EFBs and valve regulated lead-acid (VRLA) batteries, along with a very small number of lithium ion (Li-ion) batteries used in more expensive performance vehicles.”

  3. Ok, thanks. According to the EPA, each 100 lbs weight removed improves fuel economy by 1-2%. For a stop-start car, this will be at the higher end of the range since less fuel is wasted by idling, making car weight relatively more important. So for the sake of argument, say 25 lbs improves fuel economy by 1/2%, or by 0.17 MPG for a 35 MPG vehicle.
    At $4 gas, that’s a $55 savings over 100,000 miles, so you’re right, it’s insignificant. I thought it would be larger.

  4. In terms of you dismissing Li-ion, or Pike, I’d say you both did the dismissing (and you have now convinced me that you had good reason.)
    I say that because if you felt any need to question what Pike had to say, you would have backed it up with more evidence than “Pike says so.” This is what you did in your 3rd paragraph, where you not only discuss Pike’s hybrid and EV adoption projections, but also discuss Lux Research and EPA projections.

  5. Sometimes I worry about including so much detail and confirmation that I dilute the message. The future development of stop-start is going to have a number of twists and turns, but I feel more comfortable with synergistic relationships than competitive relationships. This is a huge revenue pie and when you consider that each point of market penetration is worth close to $100 million in annual revenue, there’s lots of room for many successful companies to thrive. Since I’ve never subscribed to the silver bullet theory of battery technology, I’ll be delighted if Axion is competitive.


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