Verbrugge says that one of the biggest challenges is ensuring that the batteries won’t fail in extreme climates, such as the deserts of Arizona. Conventional starter batteries already give automakers trouble in hot areas, he says. Today, they’re the car part that most commonly fails under warranty in the Southwest. “Batteries don’t like hot temperatures,” Verbrugge says. “But we’re not going to say to people in Arizona, ‘We’re not going to sell you our Chevy Volt. You can drive one, but we’re not going to give you a warranty.’ That’s not an option.”
To make up for uncertainties about the life of the battery packs, GM plans to coddle them, wrapping them in insulation and including heating and cooling systems to keep them at optimal temperatures. Questions remain about when these systems should operate, since they can eat into the energy savings that electric vehicles are supposed to provide. “Let’s say you’re charging,” Verbrugge says. “Do you run your cooling system now to keep your battery cool over black asphalt? Then your energy efficiency doesn’t look so hot. Do you do that only in Arizona? These become critical engineering issues.”
GM is also oversizing the packs, adding several kilowatt-hours’ worth of extra cells to make up for potential degradation over the life of the vehicle. That makes the packs, and the vehicle, much more expensive. “Cost is a major issue for us now,” Verbrugge says. “We’re not sure people are willing to pay.”
Indeed, the Volt and other proposed cars like it are expected to cost thousands of dollars more than conventional cars, which could limit their appeal, says Paul Werbos, a program director for the National Science Foundation (NSF), who has been promoting research on better, cheaper batteries. “I don’t expect most people are going to pay that,” he says.
Werbos and Verbrugge spoke last week at an NSF-sponsored workshop focused on improving batteries for the next generation of hybrid and electric vehicles. Speakers at the workshop emphasized that better tests for battery lifetime, combined with improvements to battery design to make them last longer, will allow automakers to use fewer batteries and cut costs.
In spite of the remaining challenges, Cesiel is encouraged by the progress that the company’s engineers have made so far and believes that the Volt will be ready for production on time. Based on its laboratory testing so far, he says, the company is “happy” with the capacity and performance of the batteries. GM also knows what the cooling system will look like and has physically integrated the pack into the vehicle. What’s more, the entire propulsion system, including the battery pack, the electric motor, and the generator, was incorporated into a test vehicle and delivered to the company’s Milford, MI, testing grounds at the end of August, just two days behind the schedule set last year. “I wouldn’t say that the battery is ready,” Cesiel says, “but we’re right on track.”