The energy burned from one gallon of gasoline is 33.7 kWh of electricity. So the 85 kWh battery has the equivalent of 2.52 gallons of gas?
Yes, but the Model S is rated at 95 MPGe (for 60kWh battery), so those 2.52 "gallons" go a long way...
Those gallon equivalents DO go a long way with the level of efficiency the Model S has! Though I hope none of us get into a major accident, but if it happens, it's much better to have the flammable energy potential of 2.52 gallons of gas, rather than 20 gallons or so!
and even better when those 2.52 gals of potential energy are segmented into sixteen or so "modules" where issues are contained to the module.