Introduction
When people compare electric cars with gasoline or diesel vehicles, two questions often come up: why are many EVs limited in top speed, and why can their range appear smaller than that of a comparable combustion-engine car? The answer starts with one simple comparison: how much usable energy each type of vehicle can carry.
In an electric vehicle, the “fuel tank” is the high-voltage battery pack. Although electric motors are highly efficient, today’s batteries still store far less energy than a modest tank of petrol or diesel when weight and volume are considered. Understanding this energy gap helps explain the differences in range, performance, and refueling speed between EVs and internal-combustion vehicles.
5 liters of petrol contain almost the same amount of energy as a 350 kg high-voltage battery.
Energy stored in petrol and diesel
Petrol and diesel remain popular because they pack a large amount of energy into a small volume. One liter of petrol contains about 9 kWh of energy, while one liter of diesel contains nearly 10 kWh.
That means a compact car with a 40-liter fuel tank carries roughly 360 kWh of energy if it runs on petrol, or about 400 kWh if it runs on diesel. In simple terms, liquid fuels still offer a major energy-storage advantage over current battery technology.
The battery equivalent in an EV
A typical high-voltage battery in a modern compact EV usually provides between 50 and 80 kWh of usable energy. The word “usable” is important, because the full physical capacity of the battery is never completely available to the driver.
Battery packs include a top buffer and a bottom buffer. The bottom buffer is usually larger because deep discharge can damage the battery. A larger buffer can improve long-term durability, but it also reduces the amount of energy available for driving. This creates a difficult trade-off for manufacturers: more protection means less usable range, while more usable range may require more battery modules, added weight, and more space.
This is also why many automakers recommend keeping the battery between about 20% and 80% charge for daily driving. Doing so increases the effective buffers and can help preserve battery health over time.
Comparing petrol, diesel, and electric power in the same car
The table below compares three versions of the same model using different energy sources. The Peugeot 208 is used as an example, but the general pattern is similar across many vehicles. All energy values are converted into kWh for easier comparison.
| Model | Energy stored in fuel tank or battery (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 |
Why EV range still looks different
With current battery technology, a typical combustion-engine fuel tank holds roughly ten times more energy than a typical EV battery. However, electric vehicles are much more efficient. The electric version in the table uses about one-third of the energy per 100 km compared with the gasoline and diesel versions.
That efficiency advantage comes from the electric motor itself. Modern electric motors can reach efficiencies above 90%, while even advanced turbocharged petrol and diesel engines usually peak around 38% to 40% thermal efficiency.
Still, efficiency alone does not fully close the gap. Based on the figures above, an EV would need about 128 kWh of usable battery energy to match the petrol version’s range and around 158 kWh to match the diesel version. In reality, the required battery would be even larger, because a bigger pack adds significant weight, which increases energy consumption. With today’s battery technology, matching the range of a comparable ICE vehicle remains difficult.
Solid-state batteries may help reduce this gap in the future. They could improve energy density and may also support faster charging, but widespread adoption is still ahead.
The next table compares how quickly energy can be added to each type of vehicle.
| Fuel type | Refueling or charging power (kW) |
| Petrol | 13,500 |
| Diesel | 15,000 |
| Electric | 270 |
Some of the fastest-charging EVs available today can accept up to about 270 kW of charging power. By comparison, refilling a 50-liter petrol tank in roughly two minutes represents an equivalent energy-transfer rate of about 13,500 kW, while diesel reaches around 15,000 kW. The difference is enormous.
EV owners can partly offset this disadvantage by charging at home or overnight, something that is not possible with a combustion-engine car. Also, because an EV’s battery is much smaller than a liquid-fuel tank in energy terms, the real-world time difference is not always as extreme as the peak power figures suggest. Even so, faster charging remains one of the most important areas for EV development.
