Why doesn't the Prius offer a plug-in option so it can run in electric-only mode? Great efforts went into making hybrid cars so they DON'T have to be plugged in. If a car is converted, it will have a negative effect on the life of the batteries and the reality is that it's likely the grid electricity being used is derived from coal, so there's not much, if any, savings to the environment. Additionally, the electric-only mode would be good for less than a mile at low speed, so the practicality of it is very limited.