In its Prius PHV, Toyota uses a different scheme: Three fans for air circulation, additional ductwork, and 42 sensors placed around the battery to monitor temperature. All makers of production EVs also employ electronic battery management systems and multiple microcontrollers to track the operation of the battery pack at every moment. Finally, they design the pack for manufacturability, so it can be more easily installed under the floor or elsewhere, rather than in a trunk or a back seat, as it might be in a backyard EV conversion.
The bottom line is that the cells are only a part of the cost of the battery pack. A 2009 report written by the National Research Council concluded that "the cost of assembling the pack is approximately the same as the cost of the cells." In other words, multiply the cell cost by two and you'll be closer to the pack cost. So, in the theoretical case of the $285/kWh cell mentioned earlier, the pack cost could easily be $570/kWh.
Still, that's not the end. There's the cost of doing business, including warranties, failures, and liabilities. "There's one price when you buy something and another when you fit it into the car," Swan told us. "The accountant walks in and says, 'We'll have so many failures and here's what it's going to cost us.' "
If you consider yourself a no-nonsense engineer, that might sound frivolous. But lithium-ion batteries have a history of overheating, and lawyers take a dim view of it when cars roll down the road like flaming chariots.
Two weeks ago, experts at Lux Research, Pike Research, and the Center for Automotive Research told us they estimate today's OEM battery costs at $800 to $1,000/kWh. In June of this year, Toyota engineers set the bar even higher. "Extra battery is about $500 per design mile, roughly speaking," noted Bill Reinert, national manager of advanced technology vehicles for Toyota. That means an extra ten miles of battery power equates to $5,000 on the price of the car. If you do the arithmetic (assuming about three miles per kWh), today's battery costs could be interpreted as $1,500/kWh.
To be sure, others have said that the costs are much lower. Many claim the Nissan Leaf batteries are now under $600/kWh. Two years ago, Tesla told us that the cylindrical 18650-style batteries in its Roadster cost $500/kWh.
The bottom line is, no one knows for sure. What we do know, however, is that the number we pull off the Internet isn't the same as an automaker's number. As amazing as some of the backyard engineering is (we wrote about it here), the economics of it aren't the same as the automaker's economics. We also know that the real experts aren't trying to spread fear, uncertainty, or doubt. Their cost numbers aren't part of a grand conspiracy.
The truth is, battery prices are just hard to figure out.