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Forums » Elegant Grid Tech Support » Reasons for voltage drop after lead-acid batteries are fully charged Collapse All
Subject Author Date
accord21 accord21 May 10, 2024 - 3:33 AM

There are various reasons for the voltage drop of lead-acid batteries after being fully charged, and these reasons cover a variety of aspects such as changes in the internal chemical reaction of the battery, the aging of the battery structure, and the conditions of use. First of all, sulfation is one of the important reasons. Long-term undercharging or over-discharging may lead to internal battery sulfation, i.e., the overgrowth of lead sulfate crystals on the negative plate. This overgrowth of lead sulfate crystals increases the internal resistance of the battery, resulting in a voltage drop. Sulfation is a common phenomenon during battery use, especially if charging is not timely after discharge. Secondly, plate grid corrosion is also a cause of voltage drop. Plate grid corrosion is the process of dissolving the material of lead on the negative plate into the electrolyte in lead-acid batteries.

The phenomenon of lead-acid battery voltage dropping fast when the battery is fully charged and left unused may be caused by a variety of factors, including self-discharge of the battery, chemical and physical changes within the battery, and environmental conditions. The following is a detailed analysis of this phenomenon.
The charging and discharging process of lead-acid batteries involves complex electrochemical reactions. When charging, the positive plate (anode) is converted from lead dioxide to lead sulfate, and the negative plate (cathode) is converted from spongy lead to lead sulfate as well. When discharged, these reactions are reversed, and the lead sulfate is again converted to lead dioxide and spongy lead.

[Self-discharge phenomenon]
1. Self-discharge : All batteries undergo self-discharge, i.e., even if the battery is not connected to any load, its charge will naturally decrease over time. The self-discharge of lead-acid batteries is usually more significant than that of other types of batteries, such as lithium batteries.
2. Chemical reaction: The self-discharge of lead-acid battery is partly caused by the internal chemical reaction, even if the battery is not working, the active substances on the positive and negative plates will react with the sulfuric acid in the electrolyte.
3. Evaporation of electrolyte: Evaporation of electrolyte can also lead to self-discharge, because the concentration of electrolyte will change after water evaporation, which will affect the voltage of the battery.

This corrosion leads to the loss of active material, which reduces the capacity and voltage of the battery. With the growth of battery use time, the degree of plate grid corrosion will gradually increase, resulting in a faster rate of voltage drop. In addition, active substance shedding also affects the voltage. With the charging and discharging cycles, the active material on the positive and negative plates may gradually fall off. This shedding reduces the capacity of the battery, which in turn affects the voltage. The speed and degree of shedding of active material is related to the battery’s operating conditions, charging and discharging methods and other factors. In addition to the above internal factors, external factors may also lead to a drop in voltage after the lead-acid battery is fully charged. For example, the impurity content of a new battery exceeds the standard may affect the performance of the battery.
The content of lead in the raw material of pole plate, the pollution in the production process, the quality of electrolyte and the dust, lead particles and lead slag in the assembly process may affect the performance and voltage of the battery. In addition, internal leakage, wet electrolyte between the poles of the battery, external leakage and the old battery aging serious, very small capacity, no storage and other factors may also lead to voltage drop. To summarize, there are various reasons for voltage drop after lead-acid battery is fully charged, and it is necessary to comprehensively consider the internal structure of the battery, the chemical reaction, the use of conditions and external factors and other aspects. In order to reduce the speed and degree of voltage drop, it is necessary to take appropriate charging and discharging methods, regular maintenance of the battery, avoid overcharging and over-discharging and other measures.