EV Battery Guide

The EV battery (sometimes called traction or high-voltage battery) is the most expensive component in the vehicle.

The battery’s capacity is measured in kilowatt-hours (kWh) and indicates the amount of electricity available to the car.

Total or usable?

Manufacturers list battery capacity as either gross (total) or net (usable).

This is confusing as some makers don’t state which is which.

  • Gross (total) – the complete capacity.
  • Net (usable) – how much capacity the vehicle is allowed to access.

Why the difference?

To maintain lithium-ion batteries in good condition, they should not be allowed to be completely empty (0% charge) or full (100% charge).

The gross capacity is not a particularly insightful spec, so it’s best to measure usable capacity.

Total vs Usable Battery Capacity

How does this work? And why?

The vehicle maintains an artificial buffer (around 2-5% of total capacity) that prevents the driver from completely draining or fully charging.

This ‘buffer’ is managed by sophisticated electronics called the Battery Management System (BMS). Even though your dashboard might say 100% – there is still some room in the battery.

When your battery ‘seems’ empty, more electricity remains. Most EVs will go into ‘snail mode’ to prevent the complete draining of the battery. Snail mode severely restricts speed to avoid stranding.

Example: Nissan listed the capacity of the Leaf (2018-) as 40 kWh. It was only in late 2022 that they started listing only usable capacity (39 kWh). Eventually, all manufacturers will list usable.

What makes EV batteries lose their capacity and why?

Lithium-ion batteries slowly lose their capacity due to two reasons:

  1. Calendar aging (a baseline level of degradation).
  2. How they are used.

How use causes wear

  1. Heat
    Early Nissan Leafs showed that without a cooling system, EV batteries degrade faster when heated.

    Newer EVs have active cooling systems. However, batteries left sitting in hot temperatures will degrade more quickly (heat speeds up the chemical reactions in a battery).
  2. Fast Charging
    The process of charging moves lithium ions and electrons around in the cells.

    Using a higher voltage results in the process happening more quickly and with more force, which can generate a lot of heat and stress the battery materials.
  3. Depth of Discharge
    Depth of discharge is how much power you use between charges.

    Battery cells last longer when depth of discharge is small. Frequent, small charges are better for the battery than one large charge (note that LFP batteries are the least sensitive to depth of discharge issues).

Just how bad is degradation?

Early Nissan Leafs suffered the worst degradation. Cars that are 8 years old have lost 25% of capacity (called State of Health). These cars have some of the earliest battery technology of the modern EV.

When I sold my 2014 Nissan Leaf in September 2022, it had done almost 90,000 km and had a 75% battery State of Health. This is a loss of about 3% per year.

If a modern EV with 450 km had a loss of 1% per year, then after 15 years, it would still have a range of 380 km.

How do I keep the battery in top condition?

If you are looking to maintain maximum value, the following is the best practice:

  • Keep charge between 20% and 80%.
  • Only charge to 100% when you are doing a long trip, and preferably charge just before you leave.
  • If you are in a hot climate, keep the vehicle in the shade.
  • Charge little and often
    Rather than running the car down to 10%, then right up again, charge each day (regular top-ups). There is extensive research on this (see references), and this may be the best you can do.
  • Drive the car!
    There doesn’t seem to be a correlation between the number of kms travelled and the battery’s state of health.

Why would I buy an EV if the battery is going to wear out?

It’s a valid question.

  • Battery technology is rapidly improving
    Some of the more recent EVs (such as the Hyundai Kona or IONIQ) are showing very little degradation after 4-5 years (and counting). The next generation (2022 onwards) can be expected to be even better.
  • Battery second-life use and recycling are also evolving fast.
    See more in the Nissan Leaf battery upgrade guide.
  • All new EVs offer a 7-8 year battery warranty
  • Even with a replacement battery, Total Cost of Ownership of the EV may still be better than a combustion car. Consider that savings from petrol could be $3000-5000 per year.

So how do know the value of an EV?

Battery degradation complicates value. Why buy an old secondhand EV for $8,000 only to replace a battery for $10,000 a few years later?

EVs are new technology and we are learning that the value of an older vehicle is defined by its battery. We’re also learning that an EV is not a direct equivalent of a combustion car.

Older cell phones had batteries that required a weekly charge. Yet we’ve learned to accept powerful smartphones that require charging every day.

Are there different types of batteries in EVs?

Almost all EV batteries are lithium-ion, and there are different lithium-ion chemistries that are named after their elements.

Common battery chemistries:

  • Lithium Manganese Oxide (LiMn2O4) — LMO (used in early Nissan Leaf)
  • Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) — NMC (used in later Nissan Leaf)
  • Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA (used in many Teslas)
  • Lithium Iron Phosphate (LiFePO4) — LFP (used in newer Teslas, BYD, and more).

LFP has become popular – it’s more tolerant of full-charge conditions. However, it has less energy density (i.e. you need a bigger and heavier battery to provide the same energy).

Do EVs have 12-volt batteries?

Yes. They use 12-volt batteries to power systems (the head unit, dashboard, etc) when the vehicle is not started. These batteries eventually need replacing just like in a combustion car.

What is the risk of a battery fire?

An EV battery has a 0.0012% chance of catching fire (compared with a 0.1% chance of a combustion car catching fire).

However, battery fires do happen and burn much hotter than combustion vehicle fires.

What causes an EV battery to catch fire?

A process called thermal runway occurs when a battery cell short-circuits and heats up uncontrollably.

EV traction batteries are made up of cells, joined together in modules. Modules are wired together to form the overall battery pack.

If one cell is severely damaged, the intense heat can then spread to other cells.

Thermal runway fires are harder to put out and require special treatment by the fire service.

See more at www.evfiresafe.com

What is the environmental cost of EV battery production?

The production of lithium-ion batteries is a mining-intensive process.

  • Mining is mostly powered by fossil fuels.
  • Battery production (most of which takes place in China) is also mostly powered by fossil fuels.

Carbon emissions from EV batteries

It’s difficult to put an exact CO2 emission figure on a battery due to the variety of materials and production facilities in use.

One of the most commonly cited sources (ref):

CO2 emissions on battery production:

61-106 kg CO2-eq/kWh

Example: 60 kWh battery produces 3.6-6.4 tonnes of CO2

This environmental burden can be lowered by consumers buying efficient EVs. Ironically mining emissions can be lowered by more mining vehicles going electric.

For example, the BMW iX M60 has a 112 kWh battery (range 566 km), and the Hyundai Kona has a 67.5 kWh battery (range 484 km). The M60 has double the amount of carbon emissions due to its battery size – but just 80 km extra range.

How is this better than a petrol or diesel car?

As the factories that produce batteries move to more sustainable energy sources, the carbon cost of lithium-ion batteries will lower.

Although BEVs have elevated production phase emissions, these are offset by decreased emissions during the use phase.

The extent of this offset is greater with a greener grid. New Zealand has a high amount of renewable electricity production, meaning low carbon emissions during the use phase of the EV.

Status 🙄: EV emissions are lower than petrol or diesel, but lots of room for improvement.

Does cobalt mining use child labour?

Cobalt is a rare, poisonous metal found in many lithium-ion batteries. It is expensive, heavy, and connected to unethical mining practices, big changes in price, and an unstable supply chain.

Yes, children routinely work in hazardous mines, including cobalt mines. The ILO strives to reduce the number of children in these mines. Note that the Congo is not the only major supplier of Cobalt – Indonesia is fast becoming a significant source.

You probably had cobalt in the all mobile phones you owned, along with laptops, and almost every other battery power device you’ve owned.

EV batteries also contain cobalt, however, this is changing.

BYD EVs and newer models of the Tesla Model 3 and MG ZS EV now use Lithium Iron Phosphate batteries (LiFePO 4 or LFP). Cobalt-free LFP batteries are increasingly becoming the battery of choice.

Status 🙁📈: Not great but improving.

Battery reuse and recycling

A product stewardship program for large batteries is currently undergoing accreditation in NZ. This is spearheaded by the Battery Industry Group.

The idea is to have legitimate reuse and end-of-life processes – using a ‘battery passport’ allowing complete tracking of the battery.

A stewardship fee would be added to the cost of the vehicle at the import stage (determined by the weight of the battery).

Status 🤔: Good things are in the pipeline, but there’s a lot to do.

References

  1. Ameli, M. T., & Ameli, A. (2021). Electric vehicles as means of energy storage: participation in ancillary services markets. In Energy Storage in Energy Markets (pp. 235-249). Academic Press. Link
  2. Preger, Y., Barkholtz, H. M., Fresquez, A., Campbell, D. L., Juba, B. W., Romàn-Kustas, J., … & Chalamala, B. (2020). Degradation of commercial lithium-ion cells as a function of chemistry and cycling conditions. Journal of The Electrochemical Society, 167(12), 120532. Link
  3. Xu, B., Oudalov, A., Ulbig, A., Andersson, G., & Kirschen, D. S. (2016). Modeling of lithium-ion battery degradation for cell life assessment. IEEE Transactions on Smart Grid, 9(2), 1131-1140. Link
  4. Emilsson, E., & Dahllöf, L. (2019). Lithium-ion vehicle battery production-status 2019 on energy use, CO2 emissions, use of metals, products environmental footprint, and recycling.
  5. Romare, M., & Dahllöf, L. (2017). The life cycle energy consumption and greenhouse gas emissions from lithium-ion batteries.
  6. Xia, X., & Li, P. (2022). A review of the life cycle assessment of electric vehicles: Considering the influence of batteries. Science of The Total Environment, 152870. Link
  7. Andersson, Ö., & Börjesson, P. (2021). The greenhouse gas emissions of an electrified vehicle combined with renewable fuels: Life cycle assessment and policy implications. Applied Energy, 289, 116621.
  8. Global Battery Alliance Rulebook (2022) – A master document outlining everything about battery production link.
  9. Battery University
  10. EVFireSafe (Australian data on EV fires).