Expect painfully s l o w charging. 12 amps at 120V is only 1.44 kw. To go from 50% to 80% will require a minimum of 21 hours. That assumes all the energy consumed is going to the charge, which never happens. If you open a door, or sit in the car, you will likely consume way more than 1.44 kw. In that case even if you are plugged in, you will still have a net drain. Honestly, charging from a 120V, 15 amp circuit, is not practical. Technically, it can work, but you will definitely not be driving very much.