This is asked a lot. 2 reasons, first is that the car runs the engine when it needs to move lubricants and diagnostics checks. It runs until warmed up. second many people report that the car runs when it is fully charged and the car is being charged with regain (going down a long hill for example) the battery can not be charged more and the energy is taken away with the ICE running. I have never had the 2nd one but like I said it is reported to happen.