Therefore, we collected nearly 100 questions from various online communities. After deduplication and categorization, we shared them with some excellent electrical engineers in the industry, asking them to answer them one by one. This resulted in this in-depth Q&A session. There are two parts; today's post is the first, and the second will be posted tomorrow. Stay tuned!
Thank you to all the car owners who participated in asking questions. We also benefited greatly in seeking answers for everyone. If you have any other questions about power batteries, please add the editor's WeChat below and let us know. We will spare no effort to find answers for you and discuss together what makes a good battery, the characteristics of batteries in different scenarios, and their range performance.
We also want to thank the engineers specializing in electrical engineering who worked tirelessly to answer our questions without wishing to reveal their names. They truly embodied the spirit of "leaving without a trace, their deeds done." These engineers are both enthusiastic and meticulous; we salute you with the nickname "the unsung heroes of electrical engineering," and we hope you enjoy it.
Below is a summary of the key points from this Q&A session, consisting of 13 questions and answers. Please enjoy. Saving and sharing this post will not only enhance the experience but also allow you to revisit it anytime.
(1) Three things to note to extend battery life
Electric Vehicle Users Alliance: What are some precautions for daily use of power batteries, and how can we maximize battery life?
The Three Sweeping Monks (San Di Dao Mo Monk): This mainly involves the following three aspects:
1) Shallow charging and shallow discharging.
Just like with mobile phones, try to avoid overcharging and over-discharging. We recommend users use a battery range of 20% to 90%, which is also the industry-standard recommended range.
2) Do not drain the battery completely when leaving it idle for a long time.
If your car only has 10% battery remaining and you're going on a long trip for more than a month, you can't just leave it there. Modern cars are quite intelligent, and some functions continue to operate even when parked. 10% battery might not be enough, and could even damage the main battery. Therefore, if your car will be parked for an extended period, it's recommended to keep the battery level around 70% to 80%; this range is more reliable.
3) Avoid charging frequently when the battery is high.
If you don't drive much each day and charge your car when it still has 80% or 90% battery remaining, keeping the battery at 100% all the time, this is bad for the battery. As mentioned above, we recommend using the battery between 20% and 90% of its capacity. Accordingly, it's better to charge it when the battery level drops below 20%.
(2) It's okay to occasionally let the battery drop to 0%.
Electric Vehicle Users Alliance: Does the battery level drop to 0%?
The Three Electric Sweeping Monk: It has an impact, but it's fine if it happens occasionally.
Batteries actually have a safety margin. It's not that if the manufacturer labels a battery as having 60 kWh, it actually only has 60 kWh. Basically, all batteries have a usable capacity that is greater than the nominal value. That's why you'll see some cars that can still run for a while after the battery has reached 0 kWh.
(3) Batteries will age over time, but short circuits are unrelated to this.
Electric Vehicle Users Alliance: Will the battery age over time and become prone to short circuits?
The "Three-Electric Sweeper Monk" (a term referring to a person who is observant and unassuming about battery technology) says: Just like mobile phones, batteries will inevitably age over time, but usage time has little to do with short circuits. Short circuits are mainly related to factors such as whether the battery has been bumped or knocked, or whether there are impurities in the battery cells.
(4) The degree of battery degradation is related to the degree of vehicle use.
Electric Vehicle Users Alliance: Will ternary lithium batteries degrade by 20% after 8 years of use?
The "Three-Electric Sweeper Monk" explains: It depends on how you use it and how much you use it. Some people can drive 200,000 kilometers in two years of commercial operation, but a typical private car will only drive 30,000 to 40,000 kilometers in two years. The degree of degradation in these two situations will definitely be different. As for how much degradation has occurred, testing is needed to determine it.
(5) Fast charging for family cars is not a big problem.
Electric Vehicle Users Alliance: Compared to slow charging, how much does fast charging affect battery life? Is this impact negligible in daily use?
The "Three-Electric System Sweeper" (a term referring to a knowledgeable person who understands electric vehicles) explains: This impact is difficult to quantify with objective data. Generally speaking, fast charging within the battery's healthy charging range will not affect its long-term performance and can meet usage quality requirements. However, frequent fast charging, as seen in some commercial vehicles, does have some impact on battery life and safety, slightly increasing the risk of spontaneous combustion. But for most family cars, which are typically fast-charged only every few days, the impact should be minimal.
(6) Theoretically, a car with a combined range of 653 kilometers would need to be driven 970,000 kilometers before its range drops to 80%.
Electric Vehicle Users Alliance: For each brand of vehicle, approximately how many kilometers would it take to reach the manufacturer's promised battery degradation level of 80%?
The "Three-Electric Sweeper Monk" says: Generally, power batteries need to go through 1500-2000 charge-discharge cycles before they degrade to 80%.
Your editor-in-chief currently drives a JFZ Alphard T with a range of 653 kilometers. Theoretically, if we calculate based on 1500 charge-discharge cycles, one cycle can cover 653 kilometers, and 1500 cycles would cover 979,500 kilometers. Even if he drives 60,000 kilometers a year, it would still take 15 years to complete. However, this is just a theoretical estimate and should only be used as a reference; the actual situation may not be so good.
In addition, the battery cycle life varies from car to car, and it cannot be calculated solely based on the number of cycles during use. Some manufacturers may also secretly lock the battery level later on, which will also reduce the driving range.
(7) Three reasons why batteries cannot be fully charged and discharge less
Electric Vehicle Users Alliance: Why does the battery not fully charge after a period of use? And why does it discharge less? For example, when the car was new, it was fully charged at 408V, but now it is only 380V; the discharge cutoff voltage is 333V and it can't run anymore, but when the car was new, it was 300V and it could still run on the highway.
The three-way expert explains: There are three situations that can cause this phenomenon: first, the battery naturally degrades; second, the battery consistency is poor, meaning the batteries need to be balanced; and third, the battery is locked.
A typical battery pack consists of over 100 individual cells, but the maximum voltage limit varies between manufacturers, and also differs between lithium iron phosphate and ternary lithium batteries. Let's assume the highest voltage of a single cell in the battery pack is 4.2V. Under perfect conditions with no damage or other malfunctions, the charging process ends at 4.2V, and the fully charged voltage reaches 408V. Similarly, the discharging process also ends at 4.2V.
However, as the vehicle is used, the battery itself deteriorates, and the maximum voltage of some individual cells drops below 4.2V, for example, to 3.9V. In this situation, cells in good condition with a voltage of 4.2V can be fully charged, but cells in poor condition cannot be fully charged. Therefore, the final overall voltage may become 380V, instead of reaching 408V. Furthermore, during discharge, the amount of electricity released depends not on the best cells, but on the worst cells—similar to the barrel principle. So, a battery that could previously discharge 408V may later only be able to discharge 308V, resulting in reduced range and decreased vehicle performance.
It should be noted that if the above situation is caused by the degradation of the battery itself, then it is irreversible unless a new battery or corresponding battery cell is replaced.
However, if the problem is simply due to excessive voltage difference, we can resolve it through battery balancing. The most common balancing methods are slow charging and balancing at a 4S store. After balancing, the battery state will be changed, the voltage will increase, and it can be restored to its original level.
Finally, if it's the third scenario, caused by a power outage, then there's no other way but for the manufacturer to release the power.
There are many ways manufacturers lock the battery now. Some manufacturers will limit the voltage at the top, reducing the voltage that is charged; some will retain the voltage at the bottom, reducing the voltage that is discharged; some may limit both the top and bottom, so that less charging at the top and less discharging at the bottom will result in a significant change in battery life.
However, the battery's AC internal resistance increases by approximately 40% when the SOC > 80%, and by approximately 35% when the depth of discharge > 80%, with the most severe deterioration occurring in the internal resistance. Therefore, a depth of discharge < 80%, and 20%...
Electric Vehicle Users Alliance: There are quite a few electric vehicle models with locked batteries now, ranging from as low as 20,000 kilometers to hundreds of thousands of kilometers. Do manufacturers have standards for how many kilometers the battery will be locked?
The Three-Electric Sweeping Monk: That's hard to answer, I can't say.
(8) To measure battery degradation, a professional inspection is required.
Electric Vehicle Users Alliance: What are the standards for measuring battery degradation?
The three-electric sweeping monk: There doesn't seem to be a national standard for attenuation, but there is a national standard for capacity testing methods.
This requires inspection by a professional automotive quality inspection agency, and third-party platforms like CATARC (China Automotive Technology and Research Center) are capable of doing so.
The test follows the national standard method: first, the battery is completely discharged, then fully charged at the specified rate, and finally, the amount of charge is calculated. However, this method is very expensive, and they may not accept individual users for testing.
(9) For ordinary users to check battery degradation, they can look at the charge level, but the loss should be removed.
Electric Vehicle Users Alliance: How can ordinary users determine if a battery has experienced significant degradation, and whether this degradation meets the manufacturer's warranty conditions?
For individual users, if the battery degradation is particularly significant, you can directly check the charging level. Note that you should not rely solely on the State of Charge (SOC), as manufacturers can easily manipulate the SOC.
However, looking at the charging amount isn't entirely accurate; losses need to be accounted for. For example, when charging in the summer, the battery needs to dissipate heat because the car is exposed to high temperatures; while in the winter, it's very cold, and the battery needs to be heated. Both heat dissipation and heating consume some electricity.
Therefore, if you want to assess battery degradation based on charging capacity, you need to find a suitable season with temperatures around 20 degrees Celsius. However, different car brands have different temperature requirements, so you need to check the specific requirements of each model.
It should be noted that judging whether a battery has degraded based on its charging level is only a reference for car owners. For legal grounds or to determine whether it meets warranty conditions, a professional inspection is likely required.
(10) There are three main types of charging losses, and the total loss is generally less than 10%.
Electric Vehicle Users Alliance: How much electricity is typically lost during fast and slow charging, and at what rate? For example, if a SAIC Roewe ERX5 has a battery capacity of 48.3 kWh, and the remaining driving range is less than 20 kilometers, how many kWh will be lost when the battery level increases from 6% to 100%?
The "Three-Electric System Sweeper Monk" explains: The losses during charging include the following components, but the exact percentages are difficult to determine:
1) Losses incurred when a large DC-DC battery charges a small DC battery.
A DC-DC converter is a device that charges a smaller battery from a larger one. It converts the 300V voltage of the larger battery to the 12V voltage of the smaller battery. Therefore, a DC-DC converter can be simply understood as a transformer.
This is an inherent loss; it occurs whenever a small battery is charged, whether it's slow charging, fast charging, or while the vehicle is in motion.
2) Slow charging has losses due to charger conversion, while fast charging does not have this loss.
3) Both fast charging and slow charging result in losses due to battery heat dissipation or heating, but fast charging results in less loss than slow charging because it takes much less time.
Generally speaking, charging loss should be within 10% under normal circumstances. However, exceptions exist, such as in winter when the temperature drops to minus 10 or 20 degrees Celsius, the charging loss will definitely be greater; or when slow charging, the charging cable is longer, which will also result in greater loss.
(11) The natural degradation of the battery will not cause significant economic losses to the user.
Electric Vehicle Users Alliance: How significant is the financial loss to car owners due to battery degradation? Will it be like a mobile phone battery, requiring replacement after two years?
The unassuming expert on battery technology: Natural degradation won't cause significant financial loss. Battery wear is related to the number of charge/discharge cycles. Mobile phones are charged once a day or several times a day, while family cars are generally charged every few days, and their large capacities are incomparable to mobile phone batteries. Therefore, it's not necessary to replace a battery every two years like a mobile phone.
(12) Battery upgrades by manufacturers are not all negative; some are positive optimizations.
Electric Vehicle Users Alliance: Why are most manufacturers' battery optimizations currently negative? For example, issues like battery lock-in.
The "Three-Electric System Sweeper Monk" explains: Battery lockout situations are quite unique and heavily limited by hardware conditions, which is unavoidable. However, allowing the battery to operate within its healthy operating range does, to some extent, benefit battery safety and lifespan.
However, it cannot be said that all battery upgrades by manufacturers are negative, because the three core technologies (battery, motor, and electronic control system) have made great progress in recent years, and many aspects can be upgraded through algorithms to provide users with a better experience. Some manufacturers' upgrades to the three core technologies can even achieve positive optimization.
(13) SOC can be faked, so some cars experience a rapid drop in range after the last 50% of their range is depleted.
Electric Vehicle Users Alliance: Some batteries are very durable in the first 50% of their lifespan, but degrade rapidly in the last 50%. What causes this? Are there any practical solutions?
The "Three-Electric Sweeper Monk" explains: This is actually related to the manufacturer's electronic control strategy. As long as the manufacturer is willing, it can be solved. The State of Charge (SOC) can be faked. For example, the entire battery may have a SOC of 60 kWh, but that doesn't mean that when the battery's SOC is 0 kWh, it is 0 kWh. When the battery's SOC is 60 kWh, the SOC is 100%.
SOC simply provides users with a value for a variable. Manufacturers can make the curve look like any other thing. It could release 40 kWh of electricity in the first 50% and 20 kWh in the second 50%; or it could release 30 kWh in the first 50% and 30 kWh in the second 50%.
However, if the manufacturer believes that most users won't use the remaining battery capacity, they can make the initial range seem very high, giving the impression that the car has excellent range performance. But if you're driving long distances, the remaining range will drop much faster.
