Causes of battery damage and repair

　　With the rapid development of the communications industry, VRLAB is increasingly being used in remote rural and mountainous areas. Due to the large area, lack of professional knowledge of maintenance personnel, and abnormal power supply, power outages are common. As a result, different defects will occur in the battery during use, especially batteries that are deeply discharged often fail early. The main forms of battery failure are: corrosion and deformation of the positive plate, softening and shedding of the positive active material, sulfation of the plate surface or lead wool, internal crystallization short circuit, etc.

　　In order to achieve higher recombination efficiency, VRLAB is generally designed with lean electrolyte, that is, the capacity of the battery is controlled by the amount of acid. This design works well in theory and in the laboratory, but it often fails prematurely in the hands of users, especially in the case of frequent power outages. When the battery is over-discharged, the electrolyte density drops to below 1.06/cm3, or even lower, causing a sharp increase in the concentration of free lead in the electrolyte, which is the root cause of battery failure.

　　2 Factors affecting battery life

　　The battery is a chemical power source. Its structure is similar. It is composed of a positive electrode, a negative electrode, an electrolyte, an insulator and a container. The active substances at the negative electrodes react chemically with the electrolyte, which plays a dominant role in the generation of current by the battery.

　　There are many factors that affect the actual service life of VRLAB, and the following aspects play a major role.

　　2.1 Effect of float charge voltage setting on battery life

　　The setting of float charge voltage has a significant impact on the life of the battery. An unreasonable float charge voltage mainly affects the corrosion rate of the battery's stop plate grid and the emission of gas in the battery.

　　2.2 Effect of balanced charging method on battery life

　　Balanced charging is to prevent some batteries from being supplemented due to inconsistency in capacity and terminal voltage. The amount of gas generated during balanced charging is dozens of times more than that during floating charging, so the charging time cannot be too long and the equalization voltage cannot be too high to avoid the surplus gas affecting the oxygen recombination efficiency, increasing water loss, and increasing the grid corrosion rate, thereby damaging the battery.

　　2.3 Over-discharge

　　Over-discharge of batteries is an important factor affecting the service life of batteries. This situation mainly occurs after the inverter power outage, when the battery pack is supplying power to the load. When the battery is over-discharged, a large amount of lead sulfate inside the battery will be adsorbed on the cathode surface, forming "sulfation" of the battery's rigid pole. Lead sulfate itself is an insulator. The more lead sulfate is formed at the cathode, the greater the internal resistance of the battery, the worse the battery's charge and discharge performance, the faster the battery capacity decreases, and the shorter its service life.

　　2.4 Effect of operating conditions on the life of VRLA batteries

　　The operating conditions of the battery also have an important impact on the battery life. If used for a long time at high temperatures, the battery life will be reduced by about half for every 10°C increase in temperature.

　　Floating charge operation is the best operating condition for batteries. The battery is always fully charged during operation. Under this condition, the battery will achieve the longest service life.

　　The battery is frequently discharged for a long time and is often deeply discharged without being fully charged, which causes the battery to be in a low-power state for a long time, and the internal plates are sulfided, resulting in a rapid decrease in capacity and battery obsolescence.

　　3. Activation and repair of outdated batteries

　　3.1 Principle of internal reaction of battery

　　The PbSO4 in VRLAB electrolyte is always in a saturated state. PbSO4 is a sparingly soluble substance. The dissolution and precipitation of lead sulfate in the electrolyte are in a balanced state. Generally, the density of sulfuric acid at the beginning of battery discharge is 1.30g/cm3, and the mass percentage concentration is 39.1%. With the increase of discharge depth, the mass percentage concentration drops to below 8.7%, and the density is below 1.06g/cm3, sometimes even lower, close to neutral.

　　The battery discharge reaction is
       

　　It can be seen from the reaction equation that sulfuric acid not only conducts current, but also participates in electrochemical reactions. During discharge, sulfuric acid is continuously reduced to generate PbSO4↓ and water.

　　After the battery is discharged, if it is not charged in time or is not fully charged, the lead sulfate produced by the discharge will crystallize and transform into irreversible lead sulfate crystals, causing the plate to sulfide and the battery to fall behind.

　　3.2 Battery Activation

　　The battery charging reaction is 

　　The charging and discharging process of the battery is to divide the pulse charging into one or several stages, and automatically charge in strict accordance with the battery charging characteristic curve. The designed charging mode is "constant current → (equalized charging and stable value) constant voltage and current reduction_ (automatic judgment and conversion to) constant current discharge" three-band type to cool the electrolyte, etc. This method is ideal and can eliminate sulfation.

　　The battery is repeatedly pulse charged and discharged at a constant current to activate the lead sulfate crystals inside it, increase the density and mass percentage concentration of sulfuric acid. As the activation and repair process deepens, the battery sulfuric acid density reaches 1.30g/cm3 and the mass percentage concentration reaches 39.1%. The dissolution and precipitation of lead sulfate in the electrolyte are in a state of equilibrium

         .

　　In the solution, the solubility rules are followed, that is

     ,

        the battery is completely repaired and the battery life is extended by one to two cycles.

　　3.3 Treatment of severely outdated batteries

　　Batteries with severe plate sulfation, electrolyte drying, short circuit between electrodes, or open circuit (severely high internal resistance, high or zero voltage) should be replaced immediately. For 2V battery packs, short-circuit the battery for emergency treatment.

　　3.4 Battery activation and repair

　　Not all outdated batteries can be repaired. There are many factors that lead to outdated batteries, which can be roughly divided into 7 types, namely plate expansion, plate corrosion, plate passivation, effective material shedding, electrolyte drying, plate short circuit, and plate sulfidation. The first 4 types are irreparable, and the last 3 types are repairable. Among them, plate sulfidation accounts for the largest proportion of factors leading to outdated batteries, up to 90%. Therefore, the success rate of repairing outdated batteries with a capacity of 40% to 80% of the rated capacity is relatively high. Tests have shown that the repair rate is as high as more than 95%; while the success rate of repairing outdated batteries with a capacity of less than 40% of the rated capacity is relatively low.

　　4 Charging settings for battery activation and repair

　　Battery activation requires repeated discharge. When charging some outdated batteries, sometimes they cannot be charged. Therefore, maintenance personnel charge them by increasing the charging voltage, thinking that the higher the charging voltage, the better, and the higher the battery can be repaired. This is a wrong understanding. This is because the water decomposition reaction is 2H2O=O2↑+4H++4e- (3)

　　If the voltage is set too high, the battery will be overcharged, and the result may be the following two situations.

　　1) If the internal oxygen recombination reaction cannot recombine oxygen in time, a large amount of oxygen and hydrogen will be released from the exhaust valve (which may even cause the battery to explode), causing the capacity to decrease.

　　2) The reaction of the positive electrode is PbSo4+2H2O=Pb02+3H++HS04-+2e. At the anode of the battery, the lead alloy and the active lead dioxide are in direct contact and immersed in the sulfuric acid solution at the same time, and each of them establishes a different equilibrium electrode potential with the sulfuric acid solution. When the battery is charged, the positive electrode consumes water due to the oxygen evolution reaction, and H+ increases, which leads to an increase in acidity near the positive electrode, accelerating the corrosion of the plate, and even causing serious corrosion of the plate, which makes the battery scrapped, and the originally repairable battery becomes an unrepairable battery. For this reason, it is recommended that the voltage during equalization charging generally does not exceed 2.35V.