A steam-electric power plant is typically between 33% and 50% efficient at producing electricty. That means that for every joule of heating value of the fuel put in, you get 0.33-0.5 joule of energy out. Internal combustion engines have an energy efficiency of 10%-50%, cars will usually be around 20%-40%.
Getting a number for how much petrol is used in a full charge of an electric car is mostly impossible. First of all, the fuel used in power plants is not petrol but coal or heavy oil (or gas), and then you have further losses that vary individually. For example transportation losses, with electricity it depends on how far the charging spot is from the next power generation, with petrol it depends on how it had to be shipped. You could also have a power plant that's combined heat & power, which means the actual fuel efficiency can be in the high nineties.
Overall, simply driving an electric car does very little for the environment if the charge comes from fossil electricity generation. However, electric cars oben the possibility of using renewable energy in a far more efficient way than producing renewable ethanol as fuel or utilizing power-to-gas processes.
There are pros and cons to the two solutions.
In order to evaluate which is more efficient between burning fuel in a plant and then supply the car with electricity or directly burn the fuel in the car you have to make a so called Well-to-wheels analysis.
This means accounting for all the energy conversions and expenditures on the two process chains from when the raw fuel is extracted from the ground to the power that actually moves the car.
This analysis should be done for every fuel, type of car, and plant, but generally speaking the PROs of an electric car are:
-Generating power in a big plant is more efficient than in a little engine.
-Distributing electricity is a fairly efficient process.
While the PROs of a combustion engine car are:
-A combustion engine converts the heat of the fuel directly into mechanical power, without the intermediate step of electricity, this increases the overall efficiency.
-There is no energy loss in storing the fuel in the tank, while on the other hand a battery incurs significant energy losses.
-The high energy density of most fossil fuel makes it so that the tank is a minor part of the total weight of the car.
Think of this:
If burning gas in a small engine was more efficient than the electricity in your house, why don't people just stop using network electricity and run generators with gas?
The answer is generally: powering cars by gas is VERY inefficient. The major contributors, roughly in order of effect on efficiency:
1. Transporting gas is very costly. Refined gas has to go to every single gas station in the nation. Powerplants operate on much more efficient scales. Electricity is delivered with few moving parts with systems that last far longer.
2. Car engines are inefficient. Car engines have to operate in a wide variety of loads and conditions. Powerplants are not at all comparable. Per unit of natural resource, powerplants produce more usable energy.
The short of it is a Tesla produces less pollution than internal combustion, *even if* the powerplant is using all coal.
Not sure if Telsa is fully electric. Assuming yes, the answer depends on geography. If you live in Europe, there likely are few fossil fuels being burned to generate electricity. If you live in China, China burns coal like there's no tomorrow.
The 65% is likely an average, maybe a global one maybe including multiple modes of transportation and genea energy use. Each country will be vastly different depending on it's energy policies.