In his latest budget proposal, President Obama wants to increase the current $7,500 tax credit available to buyers of battery cars and plug-in hybrids to $10,000 with the goal of boosting demand for the high-mileage vehicles. Critics have questioned the credits, but proponents say the credits are critical to encourage the vehicles’ development. The President set a goal of having at least one million plug-in vehicles on the road by 2014.