Causes of battery failure
Electric vehicles generally use maintenance-free lead-acid batteries with a gel electrolyte, available in 24V, 36V, 48V, and 60V versions. 36V and 48V batteries are more common, while 24V and 60V batteries are less so. A typical battery consists of two 12V cells in series: 24V (two cells), 36V (three cells), 48V (four cells), and 60V (five cells). Each 12V cell in a battery pack is connected in series with six separators, spaced 2V apart, each separator containing positive and negative plates and gel electrolyte. Battery failures are complex and can be broadly categorized into six types:
1. Overcharging can damage the battery.
Overcharging is a phenomenon that occurs when a battery is overcharged, resulting in damage to the battery's chemical and physical properties.
Overcharging is primarily caused by the charger. Modern electric vehicle chargers have safe charging voltage settings, generally set within 1.2 times the standard battery voltage. For example, for a 48V battery, the charging voltage is set within 57.2V. During battery discharge, the voltage gradually decreases. When the battery is recharged, the charger's red light will illuminate, indicating that charging is in progress. As electrical energy is continuously input into the battery, the voltage will gradually increase until it approaches or equals the charging voltage, at which point the charger's green light will illuminate, and charging will stop or trickle charge will begin. If the charger's voltage components malfunction, charging will not stop, and the charging current will continuously input into the battery, causing the voltage to rise continuously. This increased voltage will exacerbate the thermal reaction of the electrolyte, potentially causing the battery casing to deform (expand) or, in severe cases, leading to the battery exploding.
Secondly, overcharging is caused by voltage imbalance between batteries. As mentioned above, a battery pack consists of 2-5 12V batteries. When the batteries are first manufactured, the voltage of each battery is very close before they are matched together. However, after a period of use, voltage differences will appear between the batteries, which is called voltage differential. When charging an electric vehicle, the charger charges the battery pack connected in series simultaneously. The batteries with higher voltage will be fully charged first, and the batteries with lower voltage will be fully charged later or even continuously charged. Since the charger is set to charge or stop charging based on the overall voltage, the batteries that are fully charged first will be in an overcharged state. When the voltage differential is small, it has little impact on the battery. When the voltage differential is large, the batteries that are frequently overcharged will also experience accelerated electrolyte thermal reaction, until the battery is damaged.
2. Battery damage caused by low charge.
Low battery charge is a phenomenon that occurs when a battery is undercharged and its voltage is too low, resulting in excessive discharge that damages the coating on the battery plates. It's important to understand that any vehicle electrical appliance has a standard operating voltage range. Exceeding this range can easily cause short circuits or even burnout, while falling below it can prevent starting or proper functioning, and even shorten its lifespan. This applies to both vehicle electrical appliances and batteries. Many electric vehicle users charge their vehicles only every few days, and some even drive more than 60% of the new battery's rated mileage daily. It's crucial to understand that decreased battery capacity leads to insufficient battery voltage (undervoltage). Insufficient voltage cannot effectively supply the basic voltage needed for vehicle electrical appliances. When the voltage drops while the user continues to drive the electric vehicle, and the battery cannot provide the normal voltage, the load from the vehicle electrical appliances causes the battery to become undercharged. Frequent low battery charge will gradually cause the lead layer on the battery plates to peel off, eventually damaging the plates.
3. High current discharge during startup, acceleration, and overload can damage the battery.
The instantaneous current during the start-up and acceleration of electric vehicles is very large, typically reaching 20A to 50A. Depending on the motor power, the normal discharge current should ideally be controlled below 10A. Due to the excessive instantaneous current, the electrolytic reaction accelerates rapidly, inevitably affecting the electrode coating. Over time, the lead powder on the electrode plates will gradually detach due to the pull of the high current, causing the electrolyte to turn black (due to lead powder), ultimately rendering the battery unusable. Overload occurs when an electric vehicle is overloaded, such as with excessive cargo or passengers. Overload increases the battery's discharge load, and prolonged high-current discharge directly affects the electrode coating, accelerating the softening process. Poor road conditions, such as potholes, red lights, and road obstacles, also contribute to high-current discharge. Furthermore, it's worth noting that the higher the motor power of an electric vehicle, the shorter its battery life. This is because a higher motor power results in a higher discharge current, causing greater damage to the battery.
4. Sulfation of the electrode plates leads to battery damage.
What is battery sulfation? Sulfation occurs when hard, white lead sulfate crystals form on the battery plates, which are very difficult to convert back into active lead sulfate during charging. This is called sulfation. The cause of lead sulfate formation is over-discharge or prolonged storage after discharge. Lead sulfate particles dissolve in the electrolyte, reaching a saturated state. These lead sulfate particles recrystallize at low temperatures, while crystalline lead sulfate precipitates. This process of repeated growth and development on the precipitated particles due to temperature fluctuations leads to larger crystals. This type of lead sulfate has poor conductivity, high resistance, and very low solubility and dissolution rate, making it difficult to recover during charging. Therefore, it contributes to reduced capacity and shortened battery life. While sulfation is a significant factor in battery capacity reduction, damage to the battery plates from high current is an even greater cause of capacity reduction in electric vehicle batteries.
5. Water loss can damage the battery.
Water loss is one of the fundamental reasons for reduced battery capacity. Most electric vehicles use maintenance-free lead-acid batteries. Many users ask why these sealed, maintenance-free batteries still experience water loss. The reason is simple: water is a crucial component in the battery's electrolytic reaction. When a battery experiences overcharging, high-current discharge, increased internal resistance, or a short circuit, it easily generates heat and forms water vapor. Most of this water vapor is retained within the sealed battery casing, but a small portion leaks out (depending on the density of the battery casing material). Over time, the battery will lose water. Generally, electric vehicle batteries will show signs of water loss after more than six months of use; the higher the motor power, the more severe the water loss.
6. Other reasons that cause battery damage.
Besides the main causes of battery failure mentioned above, poor battery quality, plate detachment, electrolyte leakage, damaged casing, and broken battery terminals are also causes of battery failure, which will not be explained in detail here.
Battery repair methods
Battery damage is repairable, just like a person needs medical attention when sick. If it's just minor damage, such as sulfation, it can be repaired with appropriate methods. However, if it's fatal damage, such as lead powder falling off the plates, perforation, or bending, it represents a loss of physical performance and cannot be repaired. Therefore, when repairing a battery, it's essential to first determine the extent and cause of the damage and then address the problem accordingly.
(I) Battery Testing
Step 1: Check the external condition of the battery:
Check the battery's external appearance for any damage. Inspect the battery casing for bulges, leaks, breaks, or corrosion on the battery terminals. If any of these issues are present, the battery is likely dead.
Step 2: Check if the battery voltage is normal.
(1) During charging (after two hours), check the voltage of each individual battery cell three times, 20 minutes apart. If any individual battery cell has a voltage exceeding 15V, it indicates that the battery is sulfated; if the voltage consistently fails to reach 13V or above, it indicates that the battery cell is short-circuited or lagging behind.
(2) During the discharge process, use a multimeter to measure the voltage of each individual battery three times, with a 10-minute interval between each measurement. If the voltage of a certain individual battery drops faster than the other batteries and falls below 10V, and this battery has the shortest discharge time, then this battery is the problematic battery.
(3) Detect the static voltage (floating voltage) of a single battery. When the voltage is zero, there are two possibilities: one is that the battery is completely disconnected, the circuit is not open, and the voltage is zero; the other is that the battery has been left for too long, and the voltage is as low as 1-2V, or even zero.
Step 3: Check if the battery electrolyte has lost water or turned black.
Check if the electrolyte has deteriorated or lost water. After charging the battery for 3-6 hours, touch the side of each battery cell's casing. If the battery is hot to the touch, that cell is dead. If it is only hot, around 40 degrees Celsius, and the charger's red light is constantly on while charging, it indicates severe water loss. Alternatively, you can open the battery cover to check the water loss status.
Whether the electrolyte is black can directly indicate the condition of the battery plates. Open the cover on top of the battery; you will see six round holes. Check the color of the electrolyte in each hole. If it is black, it means the lead powder on the plates has detached, and the battery is faulty.
(II) A Brief Discussion on Battery Repair Methods
Battery repair is not difficult. However, repairing an entire battery pack (in series) simultaneously is challenging (excluding cases of sulfation). If even one cell in the pack has physical damage, repair equipment will be ineffective. The key is to repair each cell individually, allowing for both identification of the damage type and application of different repair methods. Therefore, the crucial aspect of battery repair is repairing individual cells (typically 12V). Below are some simple introductions:
1. Pulse Repair Method:
The best method for eliminating sulfation in batteries is the pulse repair method. When repairing a battery, the instantaneous voltage of the pulse is generally between 60V and 300V, depending on the product's intended function. For products used for battery life extension, the pulse voltage should not be too high. However, for products specifically designed for battery repair, the pulse voltage can be higher (as excessive pulse voltage can damage the battery plates). A higher pulse voltage results in a shorter repair time, while a lower pulse voltage results in a longer repair time. Although the instantaneous pulse voltage is high, the average voltage is not high, posing no harm to humans and making it very safe. From a solid-state physics perspective, any insulating layer can be broken down under sufficiently high voltage. Once the insulation layer is broken down, large lead sulfate crystals become conductive. Applying a momentary high voltage to high-resistivity insulation can also break down large lead sulfate crystals. If this high voltage is short enough and current is limited, the charging current will be small enough to prevent excessive gas evolution even after the insulation layer is broken down. The amount of gas evolution in a battery is strongly related to the charging current and charging time. If the pulse width is short enough and the duty cycle is large enough, the micro-charging that occurs simultaneously can prevent gas evolution from forming while ensuring the breakdown of coarse lead sulfate crystals. This achieves pulse-induced desulfation.
Specialized pulse generators are available on the market, but it's important to choose one with good performance. The resonance between the pulse and the battery plates is crucial, which depends on the pulse frequency and amplitude. Insufficient frequency and amplitude won't effectively eliminate sulfuric acid crystals, while excessive frequency and amplitude can damage the electrode plates and cause gas evolution. Furthermore, there are many types of pulse waveforms, which can be displayed on an oscilloscope. A good pulse wave can effectively break down the insulation layer without damaging the battery, reducing the pulverized sulfuric acid crystals back into the electrolyte. This is similar to breaking a large rock; is a pickaxe or a hoe more effective? The answer is obvious.
2. High-voltage electrical repair method:
High-voltage repair methods involve using sustained high voltage or high current during charging to repair the battery, often employed when pulse repair methods are ineffective. Firstly, the high-voltage repair method: This method primarily uses a charging voltage of 1.3-1.5 times the battery's nominal voltage. For example, a 36V battery can be charged with a 48V charger while maintaining or near the same charging current. The charging time must be carefully controlled to avoid excessive heat due to gas evolution. This method is effective for batteries with short circuits or minor plate softening, but improper use can damage the battery's contact points. Secondly, the high-current repair method: This method primarily uses a charging current 1.5-2.0 times higher than the normal charging current. For example, a 20AH battery can be charged with a 3-4A charger. The advantages and disadvantages are the same as the high-voltage repair method.
3. Full charge and full discharge repair method:
The full charge/discharge repair method involves fully charging a battery and then fully discharging it to repair it. This method is particularly effective for repairing slightly damaged batteries. It can also effectively activate the active materials deep within the battery, improving its capacity. For batteries with mild sulfation or high internal resistance, the key is to ensure a complete discharge, specifically discharging each individual cell. One to two full charge/discharge cycles can generally improve the battery's capacity. This method should not be used frequently; it should be used at least once every six months and at most once every three months.
4. Hydration and Repair Method:
Battery water loss can be repaired by adding water. The purpose is to dilute the increased concentration of sulfuric acid and allow the electrolytic reaction to proceed normally. The method is relatively simple: just open the battery cover, where you will see six round holes. Inject a certain amount of distilled water into each hole, and then soak for at least 24 hours. Only distilled water should be added; do not add other types of water, including purified water, as other types of water contain various metal molecules that can easily cause self-discharge and damage the battery.
5. Re-grouping and repair method:
Electric vehicle batteries are typically battery packs composed of several cells connected in series. Battery damage can be multifaceted, and a battery may suffer from several types of damage simultaneously. Sulfated batteries generally perform well after repair; however, batteries with softened plates or broken separators, even if repaired, have limited reuse value due to physical damage, and their lifespan after repair is extremely short, with further repairs yielding even worse results. The best approach is to replace the batteries with little repair value with older batteries that still have at least 80% capacity, and then reassemble them with the remaining cells.
Battery maintenance methods
Batteries have a limited lifespan, and battery repair only aims to maintain that lifespan to its designed limit. Claims that battery repair products can restore any damaged battery to the same condition as a new one, or guarantee a lifespan extension by a significant factor, are unscientific and unrealistic. Damage to a battery from any cause will affect its lifespan. The key is to minimize battery damage and reduce its impact on battery life. Below are some simple daily maintenance methods for electric vehicle batteries for user reference.
1. Use your vehicle and charge it daily. Lead-acid batteries don't have a memory effect. The reason for rapid capacity reduction is mainly due to sulfation, water loss, and undercharging. Batteries are most vulnerable to undercharging and low voltage. Frequent undercharging easily damages the battery plates. Our investigation found that up to 70% of electric vehicle battery capacity reduction is caused by the high current (starting current) during discharge damaging the battery plates (especially noticeable in electric motorcycles). This plate damage is a physical injury that cannot be repaired. Therefore, daily use and charging to ensure the battery always has sufficient voltage is essential.
2. Replenish with distilled water regularly. Many users mistakenly believe that maintenance-free batteries don't need water. During charging and high-current discharge, maintenance-free batteries generate heat, which causes water to evaporate. Although the evaporation process is very slow, the cumulative amount of water evaporated over time is significant. Therefore, the battery should be replenished with water approximately every 6 months to extend its lifespan.
3. Proper Starting Techniques for Electric Vehicles. Electric vehicles have a high starting current, especially electric motorcycles with high-power motors. This high current can damage the battery plates. The best method is to ride the vehicle like a bicycle before starting it, and then turn on the power. Of course, many electric motorcycles don't have a riding mechanism, in which case this method is not feasible.
Fourth, perform a deep discharge of the battery once per quarter. After a period of use, some active material will inevitably settle into the battery. If this active material is not activated in time, it will inevitably affect the battery's capacity. Therefore, when using an electric vehicle frequently, the battery should be deeply discharged once per quarter.
5. Regularly check the charger's condition. A new battery typically takes 6-8 hours to charge. The charger will light up green when fully charged. If the charging time is excessively long, check the charger's voltage protection device for damage. If it is damaged, replace the charger immediately, otherwise, it can easily damage the battery. Additionally, do not purchase fast chargers, as fast charging can also damage the battery plates.
6. If the battery is not used for an extended period, it should be charged at least once a month. This is to prevent the battery from sulfating and becoming discharged due to prolonged storage.
7. Prevent the battery from being exposed to direct sunlight. Exposing the battery to direct sunlight will cause its temperature to rise, so this should be avoided.
8. Use a battery protector as early as possible. A battery protector is also a pulse generator. Because the pulses continuously eliminate sulfation in the battery, the plates are kept clean, thus extending the battery's lifespan. However, it is not very effective against high current damage to the battery plates (for example, some electric motorcycles use chargers with pulses, but the battery life extension effect is not obvious). New technologies must be added to improve this.
The above three parts comprehensively introduce the relevant technologies and knowledge of battery damage, repair, and maintenance. This is based on our years of experience and market feedback, and the language is simple and easy for laypeople to understand. At the same time, we sincerely demystify electric vehicle battery repair technology, revealing that while many methods exist, they are not effective for all types of damaged batteries. Sulfated batteries and those with minor issues may show improvement after repair; slightly softened plates, short circuits, or broken connections may experience temporary relief after repair, like a brief resurgence before returning to their original state; and for severely damaged batteries, repair is essentially ineffective. The purpose of introducing this knowledge is to help readers gain a basic understanding of the industry and make informed choices regarding battery maintenance and repair.
