The efficiency of an electric vehicle is energy. Electric vehicles convert around 77% of the electrical energy from the grid to power at the wheels, whereas gasoline provides only 10-30%.
No, electric cars are not 100% efficient but they are more efficient than gasoline cars. Because energy loss in electric vehicles has only 15% to 20%.
70% energy efficiency means that the total energy produced to the machine only 70% is used and given as an output.
No, it is impossible to heat engines to achieve 100% thermal efficiency.