The Truth About Electric Car Batteries and How Their Wear and Tear is Not a Concern
The most important component of an electric car is the battery which is still accompanied by myths and misconceptions. The main ones of them are related to rapid wear. Here is an explanation of how an electric car battery and its charging work and why people should not worry about it.
Robert Aare
Enefit Volt Project Manager
The growing number of electric cars on the streets is a technological revolution. This especially concerns the vehicle's most critical component - the battery. The importance of the battery is directly reflected in the price of the car. While in 2015, according to Bloomberg, the price of the battery accounted for 57% of the average price of an electric car sold in the United States, then by 2019, this rate had dropped to 33%. The analyzes based largely on this factor show that the price of an electric car equivalent to a car with an internal combustion engine will be the same by 2022.
The price of the battery has fallen sharply over the last 10 years due to technological advances, but at the same time, fears have emerged that are less related to electric cars than to other everyday devices such as smartphones and laptops.
Battery life is affected by its usage and the environment
The battery life of mobile phones and laptops significantly decreases over time. The same was observed for some of the first electric cars to enter the market in early 2010s. As an example, several local governments in Estonia have sold the Mitsubishi i-MiEV arrived here within the electromobility program in 2011-2012. While it is a standard to buy a new mobile phone or laptop every 3-4 years, no such trend has been observed in the case of cars. Fortunately, the new electric cars on the market today do not need to.
The main determining factor of any battery is its capacity which tells you how much energy it is able to store. A decrease in battery life means a decrease in battery capacity. In other words, the capacity of the battery decreases over time as a result of use. This is known as active battery degradation. Passive degradation of batteries is due to temperature and time. We will talk about it later.
Batteries are designed for reversible use, i.e. they can be both charged and discharged, but each cycle leads to a loss. Some of the ions inside the battery find a place where they can no longer be “pried open”, which means that these ions can no longer be “charged”.
As a result of multiple charges and discharges, the amount of losses accumulates, resulting in a decrease in battery capacity. After a certain degree of capacity reduction, the battery will no longer be able to fulfill its original purpose. Hence the idea that each battery has a limited number of charge cycles.
Battery well-being depends on the charging speed, number, and start and end points
The problem with claiming that each battery has a limited number of charge cycles is this: each charge cycle is not equivalent to every other charge cycle. The rate of active degradation is affected by the number of charge cycles, the start and end points of the charge cycles, and the charging speed. The higher the number of charge cycles, their range and the charging or discharging speed, the faster the battery wears. Battery wear is also faster when the start or end point of the charging cycle is closer to 100% or 0% battery level. Hence the car manufacturers' recommendation to start charging before the battery drops to 10-20% and to switch between faster and slower charging.
If we always keep the charging speed the same, we will see the following relationship between the number and extent of charging cycles for a typical lithium-ion battery:
| Charging parameters | Charging cycles before reducing the capacity to 85% |
|---|---|
| 100% - 25% | 2,010 |
| 100% - 40% | 2,800 |
| 100% - 50% | 2,800 |
| 85% - 25% | 4,500 |
| 75% - 25% | 7,100 |
| 75% - 45% | 10,000 |
| 75% - 65% | 12,000 |
Source: BatteryUniversity
As you can see, using smaller charging ranges in the middle of the cycle has a good effect on battery life. Now one may ask: if you charge your car, mobile phone or laptop, does 100% battery charge level really mean 100% use of the battery capacity?
The answer is usually no. Manufacturers of battery-based devices are usually interested in a longer service life, which means that a smaller range is initially allowed for use and the rest of the battery is reserved. It is relatively widely known that the Nissan Leaf batteries use about 80% of their capacity. Also, a small amount of energy is usually stored in the battery to prevent major damage to the battery. If the car shows that its charge level is 0%, then in reality this does not mean that the battery is actually completely empty.
Electric car battery wear is not comparable to smartphone battery wear
If the battery degrades over time, the part reserved in the battery is increasingly released to maintain its capacity for as long as possible. As a result, battery degradation is not perceived in a new device for a long time. Degradation becomes noticeable when the initially reserved zone is fully released for use.
| Reserved | Virtual Battery From 0% - 100%, Range 100m | Reserved | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% | 100% |
| Reserved | Virtual Battery From 0% - 100%, Range 100m | Reserved | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% | 100% |
| Reserved | Virtual Battery From 0% - 100%, Range 100m | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% | 100% |
Source: BatteryUniversity
Another type of battery degradation is passive, i.e. battery wear due to temperature and time. As a matter of fact, the effect of temperature is dual. Cold temperatures significantly, but temporarily, reduce the capacity of the battery. Therefore, the part of battery available in cold weather is smaller. In contrast, high temperatures permanently damage the battery.
At higher temperatures, due to heat transfer, ions are more likely to accidentally find a “warm spot” where they are difficult to find. An additional concern is that the batteries heat up as a result of charging, and the faster the battery is charged, the faster they heat up. However, heat transfer is a continuous process that inevitably results in passive degradation of the battery due to time. It is just faster at higher temperatures.
All of the aforementioned degradation processes occur in lithium-ion batteries in general, including mobile phones, laptops and other devices. At the same time, the battery wear of an electric car today is not well comparable to the battery wear of a smartphone, for example. Electric cars such as the BMW i3 and Tesla have battery cooling systems to protect against the effects of high temperatures, which basically cannot fit in mobile phones. The development of battery optimization software in general, for which Estonian company Comodule is known, also has a positive effect.
For current electric car buyers, battery wear is not a concern
While the batteries of electric cars in the early 2010s seemed to wear out quickly, then in the meantime, the capacities of electric car batteries have increased significantly, so the effect of battery wear is less noticeable. The first Nissan Leaf models had 24kWh batteries (driving range approx. 170 km), while the current ones have 40kWh and 62kWh. The Tesla Model 3 battery has a capacity range of 54-75kWh with a driving range of 354-481km.
An increase in battery capacity does not necessarily mean that passive degradation is slower or faster. However, in the context of everyday use, this means that an average travel requires a smaller part of the battery, meaning a smaller discharge cycle. This in turn reduces the rate of active battery degradation. Largely for this reason, the wear and tear of the first Mitsubishi i-MiEV batteries (16-20kWh, range 130-160 km) was both noticeable and fast. No such problem has been observed with Tesla. This is evidenced by the following chart:
Source: Greencarreports.com
All in all, it can be concluded that in the context of smart solutions and evolving technology, electric car batteries are becoming larger, cheaper and their durability is increasing. To ensure the satisfaction of electric car owners, car manufacturers such as Renault (Zoe 2018: 8 years or 160,000 km) and Nissan (Leaf 2019: 96 months or 160,000 miles) grant a warranty for their batteries. Therefore, battery wear should not be a concern for today's electric car buyers.