The weighty issue of electric cars [Part 2]

The battery makes electric cars heavier than equivalent petrol cars. But the weight of EVs can come down.

This is the second part of a two-part series on electric car weights.
You can find Part One here.

Electric cars tend to be a bit heavier than an equivalent petrol car. And the average EV on the market today is heavier than the average petrol one. That’s what we learned in Part 1 of this two-parter.

Here we’re going to look at why, and whether a heavy EV fleet is inevitable.

The basic explanation for why electric cars tend to be a bit heavier is the battery. In the chart below I’ve shown the weight of various electric cars, with the battery in red.¹ The average battery weighs somewhere in the range of around 300 to 500 kilograms.

You might think that the battery is a small percentage of the total weight – less than a quarter – but it can make the difference.

The battery in a Tesla is the heaviest component of the car – as shown in the chart below.² If you’re wondering why the body of the BMW i3 is so light, it’s because it’s made from carbon-fibre reinforced plastic.

Crucially, we can compare the weight of an EV battery to the weight of the small battery and engine in an ICE. The battery in most ICEs weighs around 20 kilograms or less. The Nissan Maxima V6 has an engine weight of 120 kilograms. So the combined weight is around 140 kilograms.

That’s several hundred kilograms lighter than the battery in an average EV. Compare the non-battery-and-engine weights of EVs and ICEs, and they’re relatively similar. In fact, the EV is often slightly lighter since manufacturers try to offset the weight of the battery with a lighter frame.

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A heavier car tends to mean a bigger battery, and a longer range

A key reason why batteries have gotten heavier is that the range – how far you can travel on a single charge – has increased significantly over the last decade. As I covered in another post, the average range has almost tripled since 2011.

This increase in performance has meant bigger and heavier batteries. However, it’s not quite as simple as that: the average weight of batteries has not almost tripled as the range has. This is because there have also been massive improvements in energy density.³ This means you can get more power from a smaller battery.

Nonetheless, there is a general relationship that longer-range cars are heavier. We see this in the chart below, where I’ve plotted the range (on the y-axis) against car weight (on the x-axis). Each dot represents one EV.

Except, again, it’s not quite as simple as that. You can see a large spread of values. The cluster at the far-right are GMC Hummers: they weigh in at over 4 tonnes, and have batteries weighing 1.4 tonnes. Yet the range is pretty average, at around 480 km. You can achieve this range with a car weighing 1700 to 1800 kg.

Even beyond the extreme case of the GMC Hummer, you can find cars of the same weight with double the range. Some cars weighing 2250 kg get 400 km; others get 800 km.

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But there can be large differences in the weight-to-battery ratio

Another way to look at this data is to calculate the weight of the car per kilometre of range. Here a lower number is best. It means the car is lighter per unit of range.

I’ve calculated this ratio for each, and they’re shown in the chart. You can also explore this in an interactive chart to see each car one-by-one.

Many cars tend to cluster around the 4- to 5-kilogram mark. Multiply the car’s range by 5, and you get close to its weight. So a car with 400 kilometres would weigh around 2000 kilograms.

But you also see that these values are spread. On the low end, cars such as the NIO ET7 (a Chinese brand); Lucid Air; and some Tesla models, get less than 3 kilograms per km. At the other end, the GMC Hummers and some Mercedez-Benz SUVs are at 10 or even 12 kg. Three to four times as high.

So yes, if you want a longer range then you’ll often need a heavier battery, and most likely have a heavier car. But this is no hard rule: other factors matter too. The weight of other components in the car, and the energy density of the battery.

If you’re interested, I made the same interactive chart looking at the weight of electric cars per unit of battery capacity here.

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But a heavy car starts to limit the range and efficiency

This relationship between car weight and range generally holds true. But there’s a limit where marginal gains drop off.

A heavier car – which is inevitable from a bigger battery – reduces efficiency and affects other performance measures. You need a bigger and heavier casing to protect the battery. The body of the car increases in size.

You might increase the range by 100 kilometres, but with negative impacts on car efficiency, handling, and performance. For an EV that only gets 150 km on a single charge, that extra 100 kilometres matters a lot. For an EV that’s already getting 700 km, it’s probably not worth it.

Elon Musk made this point last year in the tweet below.

So carmarkers are keen to increase car range – increasing battery weight – but hopefully there is a ceiling, and we won’t end up in a never-ending ‘range race’.

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Why are electric cars heavier, and will this always be the case?

To bring it back to the initial question: why is the average electric car heavier than the average petrol one?

Three key reasons. 

The first is the obvious one: the battery in an EV tends to be at least a few hundred kilograms heavier than the small battery and engine in an ICE.

The second is that the EV market is much newer, and has responded to consumers’ preferences for more SUV-like cars. As I looked at in another post, the world has been moving quickly towards bigger cars. SUV sales are up almost everywhere. EV manufacturers are, as you might expect, responding to that by making bigger cars too.

This skew of the market towards higher-end cars also made sense because the initial cost of EVs has been prohibitively high for most consumers. EVs have been out of reach for many consumers at the lower end of the market. Manufacturers therefore optimised for mid-to-upper range consumers.

This SUV skew is not quite as dramatic for ICE cars because they have had decades catering to buyers across the spending range.

The final reason is the fight against range anxiety. Drivers are concerned about only having 300 kilometres, so there’s a push for 400. Then 500, and so on. The dramatic improvements in range have been a good thing. They have been essential in popularising EVs. But it has made these cars heavier over time.

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These three points matter for how the weights of EVs will change in the future; and what should be the focus if we want to stop this continued climb.

If we want to cut the weight of the battery, there are a few opportunities to do so.

1. Improved energy density in batteries. Batteries will keep getting better. This could move from a gradual improvement in the energy density of lithium-ion batteries (which are in most EVs) to a step-change improvement if solid-state batteries become available. Current lithium-ion batteries have a liquid substrate; if you take this away, you have a lighter and more energy-dense battery.
   
   Several carmakers – most notably Toyota and Honda in recent weeks – have made big claims about launching solid-state models. A word of caution, though, because they’ve made these claims before, and failed to deliver.

2. Decreased range anxiety. Improving the range of EVs over the last decade has been essential to their success. They were never going to take off with a range of 160 kilometres. But we’re now reaching the point where many EVs are hitting 600 kilometres or more. Just how much range do drivers need to feel comfortable?
   
   The marginal benefit of increasing the range further is going to fall. Hopefully carmakers use improvements in battery performance to make smaller, cheaper batteries rather than using those gains for an ever-higher range.
   
   To keep range anxiety at bay, we need to build an excellent charging infrastructure. See more on this below.

3. A growing low-to-mid range EV market
   
   The main target groups for EVs have been the eco- or technology-motivated early adopters, and the rich. This has been a good thing to get them off the ground. First, make EVs cool and desirable. Then, make smaller, more compact models that everyone else can afford.
   
   We’ve achieved stage one. Now we need to focus on stage two. If carmakers branch into low-to-mid range markets, the average weight of EVs will fall.

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   If policymakers are worried about the weight of EVs, what can they do? A few options:

1. Build excellent public charging networks

   If countries had reliable, widespread networks of fast-chargers, there would be no need to push for ever-higher range. Who needs a car with 800 kilometre range when they’re never far from a station that charges in 15 to 30 minutes?
   
   Countries should be investing a lot more in charging networks. They should be widely-available, fast-charging, and continually maintained. This is not just about reducing the weight of EVs, but about accelerating the adoption of EVs more broadly.
   

2. Incentivise low-to-mid range electric cars
   
   Governments should be doing this, regardless of the weight problem. Many have set deadlines to phase-out new petrol and diesel car sales – some countries as early as 2030.
   
   For this to go well, low-to-mid price buyers are going to need good, affordable EV options. We need more carmarkers launching smaller, cheaper models. Governments can incentivise this is various ways, such as offering larger consumer subsidies for smaller EVs, or offering tax exemptions below a given threshold.
   

3. Tax heavy vehicles
   
   The opposite of incentivising smaller, cheaper cars is penalising heavy ones. I’m reluctant to suggest this because we want electric cars to be cheaper, not more expensive, for consumers. Otherwise they go for the petrol option.
   
   Nonetheless, some countries have introduced so-called ‘SUV taxes’ (France is one example). EVs are often exempt, but if policymakers are seriously concerned about the rising weight of EVs on our roads, maybe they shouldn’t be.

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Conclusion

To round this two-part series off.

Electric cars are heavier than their petrol equivalent. This is because their battery weighs a few hundred kilograms more than the small battery, and engine in an ICE.

But a car fleet of heavy EVs is not inevitable. Climbing weights will probably turn due to battery improvements, lower range anxiety (reducing the need to push for more and more miles), and increasing uptake of EVs in low-to-mid-priced markets in the next decade.

You can get a good EV – with a more-than-sufficient range of 500 kilometres – that weighs the same as the average ICE.

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1. It was surprisingly hard to find data on the weight of the battery alone. These figures come from this article: https://measuringstuff.com/electric-car-battery-weight-with-examples/

The total weight of the car comes from My EV Reviews, which I used in Part 1 of these posts: https://www.myevreview.com/comparison-chart/weight

2. This data comes from this the following paper:

Carlstedt, D., & Asp, L. E. (2020). Performance analysis framework for structural battery composites in electric vehicles. Composites Part B: Engineering, 186, 107822.

The battery weights vary slightly from the weights given above, possibly due to them being based on slightly different models.

3. Ziegler, M. S., & Trancik, J. E. (2021). Re-examining rates of lithium-ion battery technology improvement and cost decline. Energy & Environmental Science, 14(4), 1635-1651.