Whether you are "re-charging" your car with gasoline or electricity, the procedure of transferring all of that energy is dangerous. With liquid fuel, there are the obvious flammability issues - nobody would ever consider putting a fueling station inside their home. And while electric charging is much safer, it is not perfectly safe. There are potential fire and explosion hazards from electrical malfunctions, incorrect or damaged batteries, cabling and connectors, interference from foreign objects, including rain, snow and other chemicals, and in-home hazards from wiring inadequacies and overloads. I for one would not sleep as soundly knowing that there is such a highly powered energy transfer going on in the garage attached to my house every night. Adding supersonic flywheels or redundant battery packs just increases that risk. Right now, electric vehicles are rare, and so are EV battery "events". The potential of these mishaps occurring will always be part of the risk of owning one.