General Motors announced today that it will spend $246 million on manufacturing electric motors for its hybrid vehicles–but not for its Volt extended-range electric vehicle, also called a plug-in hybrid. The move echoes its decision to build its own battery packs. Traditionally the company has focused on developing what it sees as core technologies–such as engines–in-house. Now the company is saying that batteries, electric motors, and the electronics that control them, are all core technologies going forward.

In a conference call for reporters yesterday,Tom Stephens, GM’s vice chairman for global product operations, bemoaned the lack of attention that’s been paid to electric motors. Instead, most of the attention for hybrids and electric vehicles has been focused on the battery.

But the focus on the battery actually makes sense. It’s the most expensive part of an electric car, and there’s a lot of room for improving it in terms of both cost and energy storage. In contrast, when it comes to a key metric for electric motors–efficiency–there’s not much room for improvement. Efficiencies are already in the mid 90 percent range for many electric motors, with this percentage increasing by only 2 to 3 points in last 15 years. What’s more, high-performance electric motors aren’t nearly as expensive as batteries. They cost less than engines, whereas batteries can cost twice as much–or more.

One key place for improvement is power density, says Pete Savagian, GM’s engineering director for hybrid and electric architecture and electric motors. The company’s new motors will be 25 percent smaller. Packing more power into a smaller space makes more room for the battery, transmission, and so on, making it easier to design electric vehicles and hybrids.