Introduction
Anyone researching electric vehicles for the first time usually ends up asking two very reasonable questions: "Why are the top speeds of most EVs electronically restricted?" and "Why can't an EV match the driving range of a comparable petrol or diesel car?"
Getting to the bottom of these questions requires a closer look at how much energy different fuels actually contain, and how that compares to the energy stored inside the high voltage battery pack that drives the electric motor (or motors) of an EV.
Merely 5 liters of petrol pack roughly the same energy as a high voltage battery weighing 350kg
How much energy do petrol and diesel hold?
The best place to start is with the two fuels that dominate roads across the globe today. Every liter of petrol stores approximately 9 kWh of energy, whereas a liter of diesel comes in at nearly 10 kWh. To make these figures more tangible, consider a standard compact car fitted with a fairly small 40-liter fuel tank. Filled with petrol, that car is hauling 360 kWh of energy; with diesel, that figure climbs to 400 kWh.
How much energy does a high voltage battery hold?
Modern compact electric vehicles typically come with a high voltage battery offering somewhere between 50 and 80 kWh of net usable energy. The word "net" matters a great deal here, since the full capacity of the battery is never entirely accessible to the drivetrain. Every pack requires a buffer at both the top and bottom of its charge range. The top buffer tends to be smaller than the bottom one, because allowing a high voltage battery to discharge too deeply can cause serious damage — which is why manufacturers leave a larger safety margin at the lower end. As a rule of thumb, the bigger the buffer, the greater the battery's longevity. This creates a genuine engineering headache: enlarging the buffer reduces the energy available to actually drive the car, forcing manufacturers to compensate with additional modules that add both weight and take up precious space. Buffers are such a critical consideration that manufacturers advise owners to keep everyday charging between 20% and 80%. Simply by adopting these charging habits, drivers effectively expand both buffers themselves.
Pitting the propulsion systems against each other
The table below lines up three different propulsion methods — petrol, diesel and fully electric — within the very same car, showing the equivalent energy content of each "fuel". The Peugeot 208 serves as our example, though figures for other multi-fuel models follow a similar pattern. All values have been converted into kWh so they can be compared directly.
| Model | Fuel tank energy content (kWh) | Energy consumption WLTP (kWh/100 km) | Range (km) |
| Peugeot 208 1.2 PureTech 130 PS EAT 8 | 396 | 47.7 | 830 |
| Peugeot 208 1.5 BlueHDi 102 PS | 410 | 40 | 1025 |
| Peugeot e-208 136 PS | 45 | 15.4 | 292 |
Final thoughts
Given the current state of battery technology, the fuel tank of a conventional combustion engine car stores close to ten times the energy of a standard EV battery. What works in the electric car's favor, however, is its dramatically better efficiency. As the table clearly demonstrates, the EV requires roughly three times less energy to travel the same distance as its combustion-powered sibling. This comes as no surprise when you consider that an electric motor can operate at efficiencies of up to 94%, while even the most advanced turbocharged, direct-injection petrol and diesel engines top out at around 38-40%. So what would it take for an EV to deliver a truly comparable range? Based on the figures above, matching the petrol version calls for 128 kWh, while equaling the diesel demands 158 kWh. In reality, the requirement would be even greater, because a battery of that size would add a tremendous amount of weight, pushing electricity consumption higher still. The conclusion is clear: with today's battery technology, reaching range parity with an ICE vehicle is practically out of the question. That said, early signs point to solid state batteries as a technology capable of closing much of this gap — and they could prove just as transformative for another closely related challenge: charging speed.
The table below illustrates just how different "charging" power is between the various fuels.
| Fuel type | Charging/Refill power (kW) |
| Petrol | 13,500 |
| Diesel | 15,000 |
| Electric | 270 |
The most sophisticated electric vehicles available today can take on charge at rates of up to 270 kW. By comparison, refilling a 50-liter tank equates to a "charging" power of 13,500 kW for petrol and 15,000 kW for diesel — a consequence of the fact that filling up an ICE vehicle takes only around 2 minutes. Once again, the gap in "refueling" speed is massive, and it heavily favors the combustion engine car.
Of course, this disadvantage can be softened somewhat by plugging in an EV overnight while it sits unused — an option simply not available to ICE owners. On top of that, because the EV "tank" is so much smaller to begin with, the real-world difference in total refueling time is far less dramatic than the raw charging rates imply. Even so, there's no doubt that charging needs to get faster still — and thankfully, the next generation of charging technology is just around the corner.
