Using computer models developed by Argonne National Laboratory, the [Carnegie-Mellon University (CMU)] researchers's goal was to find the optimal level of vehicle electrification that provided the most environmental benefit for the least dollars spent to reduce greenhouse gas emissions. They found that the smaller the battery pack, the greater the benefit when comparing the cost of vehicle acquisition and the amount and type of energy used to power it. That battery capacity "sweet spot" at the moment is sufficiently sized battery to propel a vehicle around 25 miles, and up to 50 miles, though the smaller the better, for now. This outcome is based on assumptions about the cost of battery technology and the price of petroleum; as the two converge, CMU's conclusions will also shift. The higher the price of a gallon of gasoline and the lower the cost of battery technology, the more larger battery-pack[s] make sense.

The Prius PHV plug-in hybrid with its 12 miles of pure EV range would be at the low end of the battery size range, the Volt at the higher end. Another critical, scenario altering factor is the composition of energy used to create electricity. The larger percentage of coal being used to generate electric power, the harder it is to make a purely environmental case for the Nissan LEAF, and other all-electric cars. For any electric-drive vehicle to make a meaningful contribution to solving the climate issue, the electric power grid needs to become dramatically less carbon intensive.