Efficiency
The internal combustion engine is not a particularly efficient machine. I have seen references that put average efficiencies at 20% and extremes of 45% (not likely).
Internal combustion engines are most efficient while operating at constant speed and steady load. That’s why car fuel efficiencies are highest for highway driving. Acceleration and load variation reduce efficiency significantly.
Electric motors on the other hand can easily achieve efficiencies of greater than 90%. Acceleration of an electric motor is also highly efficient and produces better torque characteristics than internal combustion engines. The low-speed torque characteristics are what makes electric motors the only suitable option for trains.
Not only are electric motors good for acceleration but they can generate energy when they slow down. Instead of wearing out brakes, the electric-powered vehicles can generate power and actually recharge the battery while decelerating.
Continuous advancements in electronic motor controls have helped to put EVs in the mainstream of urban transportation.
An urban environment where vehicles are frequently changing speed are far better suited for electric vehicles than internal combustion types when energy efficiency is the primary consideration.
Operating cost
The operating cost of internal combustion and EVs are quite different. Internal combustion based vehicles will require more frequent maintenance like oil changes, filters, belts, hoses, brakes, sensors, spark plugs etc. The cost of fuel is the largest single item for most owners. Fuel prices have risen significantly over the last 10 years and have nowhere to go but up.
EVs have fewer moving parts and less reliance on conventional brakes. Regular maintenance is minimal. The cost of recharging an EV is less than 15% what it cost for the equivalent gasoline consumption in June of 2018. Some jurisdictions have free charging stations in public spaces. The savings due to fuel cost could be up to $1,800 per year if you drive 15,000 km.
The single most impactive maintenance item for an EV is battery replacement. A reasonable approximation of battery life would be 8 years. The overall vehicle will have a much longer useful life, making it highly likely that there will be a battery replacement within the EV life-cycle.
According to Green Car Reports, the cost of replacing the high-capacity battery in the Chevrolet Bolt is $15,734 US. That would be a killer for most consumers for a vehicle that is more than halfway through its life. The Nissan Leaf battery is much smaller but will still set you back $5,500 US.
In this simple comparison, the operating cost for an EV is considerably less than an internal combustion engine type for the first 8 years. After that it will depend on how long the EV lasts as you try to recover the battery replacement cost. The comparison is highly sensitive to the cost associated with fuel.
Derek