Let me channel my inner Thunderf00t here. A Tesla Model S has about 85 kilowatt-hours of energy in its batteries at full charge. - https://en.wikipedia.org/wi

Let me channel my inner Thunderf00t here. A Tesla Model S has about 85 kilowatt-hours of energy in its batteries at full charge. - https://en.wikipedia.org/wiki/Tesla_Model_S#Battery https://en.wikipedia.org/wiki/Tesla_Model_S#Battery That is 85 * 60 * 60 * 1000 = 306 megajoules or 3.06 * 10 ^ 8 joules. According to Atomic Rockets' Boom Table, This is slightly less than a 54kg high explosive Iowa battleship main gun shell. - http://www.projectrho.com/public_html/rocket/usefultables.php#id--The_Boom_Table http://www.projectrho.com/public_html/rocket/usefultables.ph... - https://en.wikipedia.org/wiki/Iowa-class_battleship https://en.wikipedia.org/wiki/Iowa-class_battleship This matters because with a battery, it's Very Hard(tm) to get the energy to discharge at a high enough rate to cause catastrophic effects, like for example why Mike Tyson can punch with ~1600 Joules (uncited, popularly referenced), about the same as a 5.56mmx45mm round fired from an M16/AR-pattern rifle. Because the Joules are distributed over space (bigger cross section) and time (slower impact), Mike Tyson's punch doesn't immediately shred your tissue and bones. However, it's Very Easy(tm) to get a flywheel to have a tiny mechanical failure that causes the entire thing to release all its kinetic energy rapidly. Additionally, there's no conversion penalty with the flywheel. So the battery under catastrophe can and generally does shed its energy relatively slowly as rapidly-dissipating heat (see videos of cell phone batteries on fire), whereas a rotating wheel that just fell of its drive shaft is... markedly different. Conclusion: Even if the flywheel only holds enough energy for a single charge, it would have to be buried far underground and still might create a crater in the gas station asphalt it sits underneath when (not if) mechanical failures happen. Therefore, this is dumb and won't happen. Please help me understand where I'm wrong :)