Why a Tank of Fuel Feels Bigger Than an EV Battery

If you've ever stepped into an electric vehicle (EV) after years of driving petrol cars, you've probably noticed something curious: an EV battery can look tiny compared to a fuel tank. A 60-litre petrol tank seems to last forever, while a 70–90 kWh EV battery feels like it disappears much quicker. Add to that the fact that simply turning on the air-conditioning in an EV reduces the estimated range immediately — something you rarely notice in a petrol car — and it feels like the maths doesn't add up.

The explanation comes down to two things: energy density and efficiency.

Fuel is a miracle product - but it's had its time!

Petrol contains about 34 MJ per litre, which is roughly 9.5 kWh of chemical energy. Diesel is slightly higher again.

But internal combustion engines (ICEs) are inherently inefficient. Typically, only 20–40% of that energy becomes useful motion. The rest is lost as heat through the engine, exhaust, cooling system and drivetrain.

Fuel Tanks vs EV Batteries

Let's compare storage directly:

Type	Raw Energy	Usable Energy
55-litre petrol tank	~520 kWh	~165 kWh (≈30% efficiency)
Modern EV battery (95 kWh gross, ~86 kWh usable)	~86 kWh	~77 kWh (≈90% efficiency)

So yes — a petrol tank still carries more usable energy than most EV batteries. That's why combustion cars often appear to have greater range. But the gap is far smaller than the raw numbers suggest, because EVs waste very little energy.

Why EV Range Drops When You Turn on the Air-Conditioning

This is where efficiency becomes visible.

In a petrol car, the air-conditioning might draw 2–3 kW. Compared to the 20–30 kW of energy constantly wasted as heat, that extra load barely registers.

In an EV, the same 2–3 kW comes straight from the battery. When you only have 70–80 kWh usable, that's a 3–5% energy hit per hour, so the range estimate responds immediately.

Cost per Kilometre: Petrol vs Electricity

This is where EVs pull away decisively.

Petrol vehicle example

• Fuel economy: ~10 L/100 km
• Fuel price: $2.16/L
• Cost per 100 km: $21.60
• Cost per km: ~22 c/km

EV example

• Energy use: 0.22 kWh/km
• Electricity price: $0.32/kWh
• Cost per km: ~7 c/km

To travel ~684 km:

• Petrol: ~65 L → $142
• EV: ~150 kWh → ~$47

That's roughly one-third the cost, even before considering solar charging, off-peak tariffs or workplace charging.

What If Every Car in Australia Went Electric?

Australia has about 20.1 million vehicles. If each had an 86 kWh battery and charged once per week:

• Weekly demand: ~1.7 TWh
• Annual demand: ~90 TWh

Australia currently uses around 220 TWh per year, so full electrification would add roughly 40% to total electricity demand.

That sounds large, but:

• The transition will occur over decades
• Smart charging shifts demand to off-peak hours
• EVs can support the grid via vehicle-to-grid (V2G)
• Renewable generation is scaling rapidly

It's a planning challenge — not a roadblock.

The Takeaway

• Petrol contains a lot of energy, but most of it is wasted
• EVs store less energy, but use it far more efficiently
• Small loads feel bigger in EVs because efficiency makes them visible
• EVs are dramatically cheaper to run per kilometre
• Large-scale EV adoption is manageable with smart energy planning

References & Sources

1. Energy Education – Joule & Energy Units
   https://energyeducation.ca/encyclopedia/Joule
2. Quora – Energy Released by Burning 1 Litre of Petrol
   https://www.quora.com/How-much-energy-is-released-by-burning-1-litre-of-petrol
3. U.S. Department of Energy – Electric Vehicle Efficiency
   https://www.energy.gov/eere/vehicles/articles/all-electric-vehicles
4. Australian Bureau of Statistics – Motor Vehicle Census
   https://www.abs.gov.au/statistics/industry/tourism-and-transport/motor-vehicle-census-australia/latest-release
5. EcoGeneration – Powering the Grid Through Electric Vehicles
   https://www.ecogeneration.com.au/powering-the-grid-through-electric-vehicles/