As a widely used energy storage device, lead-acid batteries play a crucial role in various fields, such as automotive starting, electric vehicle power supply, and backup power systems. However, with the increase in service time, lead-acid batteries inevitably experience capacity fade, which not only impairs their performance but may also cause equipment failure. Therefore, exploring effective methods to slow down the capacity fade of lead-acid batteries holds significant practical importance.

Causes of Capacity Fade in Lead-Acid Batteries

The working principle of lead-acid batteries is based on chemical reactions between the active materials on the positive and negative plates and sulfuric acid in the electrolyte. During the charge-discharge process, lead dioxide (PbO_2) on the positive plate and lead (Pb) on the negative plate react with sulfuric acid (H_2SO_4) to form lead sulfate (PbSO_4). When the battery discharges, lead sulfate gradually accumulates on the plates, while during charging, an attempt is made to reduce the lead sulfate back to the original active materials.

Deep discharge is one of the key factors contributing to the capacity fade of lead-acid batteries. When the battery is over-discharged, the amount of lead sulfate generated on the plates increases significantly, and these lead sulfate crystals may become coarse and difficult to be fully reduced in subsequent charging processes. Long-term deep discharge damages the structure of the active materials on the plate surface, reducing the effective area available for electrochemical reactions and thereby leading to a decline in battery capacity. For instance, in electric vehicle applications, frequently draining the lead-acid battery to a very low level accelerates capacity fade, resulting in a gradual reduction in the vehicle's driving range.

Charging voltage also has a significant impact on the capacity of lead-acid batteries. Excessively high charging voltage causes excessive gassing inside the battery, leading to substantial loss of water in the electrolyte and accelerated plate corrosion, which severely impairs battery performance and lifespan. Conversely, excessively low charging voltage fails to fully charge the battery, and prolonged undercharging also causes plate sulfation, gradually reducing battery capacity.

Methods to Slow Down Capacity Fade

Avoid Deep Discharge

1. Reasonable Control of Depth of Discharge: When using lead-acid batteries, it is essential to avoid complete discharge as much as possible. It is generally recommended to recharge the battery when the remaining capacity is between 20% and 30%. For example, for electric vehicle users, when the instrument panel indicates that the battery level is approaching this range, they should promptly find a suitable location to recharge instead of continuing to ride until the battery level is extremely low. This approach effectively reduces the frequency of deep discharge, protects the active materials on the battery plates, and maintains battery capacity.

2. Adopt Shallow Charge-Discharge Mode: Shallow charge-discharge refers to recharging the battery before it is fully discharged and not necessarily charging it to 100% each time. This mode helps reduce the accumulation of lead sulfate on the plates and ensures more stable electrochemical reactions inside the battery. Taking automotive starting batteries as an example, if the vehicle is frequently used for short-distance trips, the battery often cannot be fully charged. In such cases, adopting the shallow charge-discharge mode—ensuring the battery can meet the vehicle's starting and short-term power needs—is effective in extending battery lifespan and slowing down capacity fade.

3. Over-Discharge Protection Measures: A Battery Management System (BMS) can be installed to provide over-discharge protection for lead-acid batteries. The BMS continuously monitors parameters such as battery voltage, current, and capacity. When it detects that the battery capacity is about to reach the preset over-discharge threshold, it automatically cuts off the circuit to prevent over-discharge. Lead-acid battery banks used in some communication base stations are equipped with advanced BMS, which effectively protects the batteries and reduces capacity fade caused by over-discharge.

Maintain Appropriate Charging Voltage

1. Select a Suitable Charger: Lead-acid batteries of different specifications require matching chargers, and the output voltage of the charger must comply with the rated charging voltage requirements of the battery. For example, a common 12V lead-acid battery typically requires a charging voltage ranging from 13.8V to 14.4V. Using a charger with excessively high or low output voltage will damage the battery. Therefore, when purchasing a charger, it is crucial to carefully check the product manual to ensure compatibility with the battery.

2. Monitor Voltage During Charging: During the charging process, close attention should be paid to changes in the battery's charging voltage. Professional voltage monitoring equipment, such as a multimeter, can be used to measure the voltage across the battery terminals at regular intervals. If the charging voltage deviates from the normal range, timely inspection of the charger or battery for faults is necessary. For example, if the charging voltage continuously exceeds the upper limit of the normal range, the voltage regulation circuit of the charger may be faulty, requiring immediate repair or replacement to prevent damage from excessive voltage.

3. Optimize Charging Algorithms: Some advanced chargers adopt intelligent charging algorithms that dynamically adjust the charging voltage and current based on the real-time state of the battery. For instance, in the initial stage of charging when the battery capacity is low, a relatively large current and appropriate voltage are used for fast charging to shorten the charging time; when the battery capacity is close to full, the charging voltage and current are gradually reduced to avoid overcharging. This optimized charging algorithm better protects the battery and slows down capacity fade. Such intelligent charging algorithms are widely used in high-end electric vehicle chargers, improving battery charging efficiency and lifespan.

Other Auxiliary Measures

In addition to avoiding deep discharge and maintaining appropriate charging voltage, several other measures contribute to slowing down the capacity fade of lead-acid batteries.

1. Control Charging Temperature: The optimal charging temperature for lead-acid batteries is generally around 25°C. Excessively high temperatures accelerate internal electrochemical reactions, leading to increased plate corrosion and electrolyte water loss; excessively low temperatures increase battery internal resistance and reduce charge acceptance. Therefore, during charging, the battery should be placed in an environment with a suitable temperature as much as possible. For example, in high-temperature summer, the battery can be charged in a well-ventilated and cool area; in low-temperature winter, charging equipment with a heating function can be used or the battery can be properly preheated to ensure charging efficiency and battery lifespan.

2. Perform Regular Equalization Charging: For lead-acid battery banks composed of multiple cells, differences between individual cells may lead to undercharging or overcharging of some cells during long-term use. Regular equalization charging balances the capacity of individual cells, preventing the performance of the entire battery bank from being affected by individual cell issues. It is generally recommended to perform equalization charging on the battery bank at regular intervals (e.g., every 1-2 months), with the charging time and voltage set according to the specific specifications of the battery bank and the user manual.

3. Maintain Battery Cleanliness: Dust, dirt, and electrolyte leakage on the battery surface can cause corrosion of the battery terminals, increase contact resistance, and impair the charge-discharge performance of the battery. Therefore, the battery should be cleaned regularly: the surface can be wiped with a clean damp cloth to ensure the terminal connections are clean and dry. Meanwhile, check for damage to the battery case or electrolyte leakage, and promptly address any issues or replace the battery if necessary.

The capacity fade of lead-acid batteries is a complex process affected by multiple factors. By avoiding deep discharge, maintaining appropriate charging voltage, and implementing other auxiliary measures, the capacity fade of lead-acid batteries can be effectively slowed down, their lifespan extended, and their performance improved—thereby better meeting the needs of various application scenarios. In practical use, users should reasonably apply these methods based on the specific conditions of the battery and the operating environment to achieve scientific maintenance and management of lead-acid batteries.