When the Ford Focus Electric debuts late in 2011, it will now have a feature in common with the Chevrolet Volt besides the LG Chem lithium polymer cells. Ford has confirmed that the Focus will use a liquid cooled battery pack with automatic thermal management, just like the Chevrolet.
Ford has opted for the active thermal management in order to help maximize the lifespan and performance of the battery. By stopping the battery from overheating, the system can help prevent the cracks that develop in the electrodes. Those cracks eventually reduce the pack's ability to hold a charge. Conversely, warming the cells when cold will improve the pack's winter performance. When the vehicle is plugged in, the thermal management will use grid power to precondition the battery before charging actually starts.
So far, Nissan and Mitsubishi are the only major EV manufacturers that are sticking with passive air cooling for plug-in vehicles. Nissan has committed to an eight-year warranty, but it remains unclear how well the battery will hold up in regular use in differing climates. Tesla's Elon Musk certainly doesn't think much of Nissan's pack.