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AGM battery, or absorbed glass mat battery, is a high-performance energy storage battery widely used in various electronic devices.
AGM battery self discharge rate refers to the rate at which the battery power gradually decreases due to internal chemical reactions and material diffusion in the open circuit state. This indicator is one of the important indicators to measure the performance of the battery and is of great significance for the use and maintenance of the battery.
What is self discharge?
Among various battery types, AGM batteries are known for their low self-discharge rate. Understanding the agm battery self discharge rate helps users effectively store and maintain their batteries for extended periods.
Self-discharge refers to the state in which the charge of the battery gradually decreases when it is not in use. In most cases, self-discharge cannot be eliminated, but it needs to be managed. Excessive self-discharge rate may limit the potential application of the battery.
Physical self-discharge
Physical self-discharge is caused by the same physical reaction as normal discharge in the battery. Electrons still move through the electrolyte, but the movement speed is much slower than normal discharge. In addition, the capacity lost due to physical self-discharge can be reversibly compensated.
Chemical self-discharge
Chemical self-discharge is the capacity loss caused by irreversible reactions inside the battery. The capacity lost due to chemical self-discharge is irreversible and cannot be compensated.
While all batteries experience some level of energy loss over time, the agm battery self discharge rate remains significantly lower due to its valve-regulated sealed design, reducing the impact of chemical self-discharge.
What is an AGM battery?
AGM battery, or Absorbent Glass Mat Battery, is a valve-regulated sealed lead-acid battery that uses a glass fiber diaphragm to absorb sulfuric acid electrolyte. This design not only gives AGM batteries low manintenance cost but also shows a relatively low agm battery self dischrage rate. These are one of its many advantages and the following will display more about AGM batteries.
Features of AGM batteries
Structure and working principle of AGM battery is the electrolyte of AGM batteries exists in the form of sulfuric acid aqueous solution. The porosity of the glass fiber diaphragm is as high as 90%, which effectively absorbs the electrolyte and reduces the risk of liquid leakage.
The lean liquid design ensures that the battery can still be used safely in various tilting states without leakage.
Performance advantages
AGM batteries have high cycle charging capacity, long service life, and high capacity stability throughout the entire service life.
Its low temperature performance is more reliable and suitable for use in a variety of environmental conditions.
Low maintenance requirements, basically maintenance-free, suitable for application scenarios that require frequent charging and discharging, such as emergency lighting and UPS systems.
Why is self discharge important to batteries?
Self-discharge can significantly limit the storage life of batteries. The self-discharge rate can be affected by ambient temperature, the battery's state of charge, battery structure, charging current, and other factors. Primary batteries tend to have lower self-discharge rates than rechargeable chemistries.
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Reduced Available Capacity
Self-discharge directly results in a decrease in the available capacity of the battery, especially for devices that need to be powered for long periods of time, such as emergency lighting and UPS systems. If the battery self discharges too quickly during idle time, it may cause the device to fail to start or operate properly. For AGM batteries, they have a lower self-discharge rate compared to traditional lead-acid batteries, ensuring better energy retention during storage. Monitoring the AGM battery self discharge rate is crucial to prevent excessive energy loss over time.
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Impact on Device Performance
As self-discharge increases, the battery's voltage gradually decreases, which may affect the performance of devices that rely on stable voltage operation. In some cases, excessive self-discharge may also trigger the battery's over-discharge protection mechanism, making the battery unable to be recharged and used again. In that case, the agm battery self discharge rate directly affects how long the battery can maintain its charge when not in use, making it a crucial factor in long-term storage applications like backup power systems.
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Storage and Usage Management
Understanding the self-discharge rate can help users better manage and maintain the battery. When storing for long periods of time, choosing the right environment (such as low temperature) can slow the self-discharge rate, thereby extending the battery's service life. In addition, regular charging and monitoring can also effectively reduce capacity loss caused by self-discharge.
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Consistency and safety
Inconsistency in self-discharge can cause different batteries in the same group to have different states after storage, which not only affects the overall capacity, but may also cause safety hazards. Therefore, reducing the consistency of self-discharge is an important part of improving battery pack performance during design and manufacturing.
AGM batteries generally have a low self-discharge rate of about 2% per month. This means that when idle, the battery can maintain a charged state for a longer time.
Compared with traditional flooded lead-acid batteries (self-discharge rates can reach 8%), AGM batteries are designed to retain energy more effectively when not in use.
Factors affecting AGM battery self discharge rates
Temperature
Ambient temperature has a significant effect on the self-discharge rate. High temperatures accelerate chemical reactions and increase the self-discharge rate, while low temperatures help reduce this rate.
Battery state
The charge state of the AGM battery also affects the self-discharge. If the battery is partially discharged, self-discharge may be faster, so maintaining a proper charge state is key.
Measuring self discharge rates
When evaluating battery performance, the agm battery self discharge rate can be assessed through multiple methods, including open circuit voltage measurement, capacity retention tests, and BMS monitoring.
Open Circuit Voltage Method
This method first fully charges the AGM battery and then leaves it to rest for 24 hours without a load. Afterwards, use a multimeter to measure the open circuit voltage (OCV). If the voltage drops, it means that the battery has lost some energy due to self-discharge. This method is simple and easy to use, but it requires a long resting time and is greatly affected by factors such as ambient temperature.
Capacity Measurement Method
In this method, the AGM battery is first fully charged and discharged to determine its initial capacity. Then, after a period of rest, it is discharged again to measure the remaining capacity. By comparing the two measured capacities, the self-discharge rate can be calculated.
Current Counting Method
The battery's charge and discharge status can be monitored in real time using a battery management system (BMS). This method accurately calculates the self-discharge rate by recording the current flowing in or out during the resting period, and is suitable for applications that require high-precision monitoring.
Accelerated Aging Test
Accelerated aging tests are performed under a controlled environment to monitor battery performance changes by simulating actual usage conditions. This method can provide insights into long-term self-discharge trends.
Conclusion
In summary, the AGM battery self discharge rate is not only affected by the battery manufacturing process and material selection, but also closely related to storage conditions and use environment.
Therefore, when using AGM batteries, we need to fully understand AGM self discharge rate characteristics and take corresponding measures to reduce the self-discharge rate in order to extend the battery life and improve the performance of the equipment. Therefore, understanding and monitoring the self-discharge rate of AGM batteries is crucial to ensure the performance and service life of the battery.
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