Sigh... I'm going to have to be a unit nazi.

Power is the rate of energy transfer and is in kW. If 1kW flows for 1 hour it's 1 kWh (power x time). A US 120V socket at 12 Amps is just under 1.5kW. A 240V socket will be double that.

1.5kW for 12 hours is 18kWh. That's not half a battery, as most cars start at 60kWh batteries now. 18kWh will get 54-72 miles depending on the consumption of the car.