Theoretically, nothing should happen but it is only a theory that depends on the car brand (all electronics). In my Mercedes W212, the ignition is cut off automatically after 5 minutes if the START ENGINE button is not pressed. The key remains in the port but the ignition is cut off and inactive until the key is reinserted.
If you often have to charge various devices (navigation, telephones, etc.), make a direct connection to the cigarette lighter. It's only 20min work. Currently, you probably have power supply "after the ignition" that I will say so badly. You cut off the plus lead (powering the lighter) and lead a new one through the battery compartment (giving an additional fuse in this circuit e.g. 2A, 5A).
