Mastering the battery state of charge(SoC) and battery state of health (SoH) of a battery is crucial for ensuring efficient operation and extending its lifespan.
This article will delve into the concepts of SoC and SoH, their interrelationships, and how to optimize these parameters through best maintenance practices.
Table of Contents
Part 1: Understanding state of charge (SoC) of the Battery
Understand battery state of charge
The State of Charge (SoC) of a battery measures the ratio of its current charge to its maximum charge. For example, it is like a car’s fuel gauge, which can display how much battery power is left and when it needs to be charged.
Whether it’s electric vehicles, smartphones, or home energy storage systems, SoC is the core parameter of battery systems.
By mastering SoC, users can better manage energy consumption and plan charging schedules.
Even when the battery is not in use, its SoC will gradually decrease, a phenomenon known as self discharge.
The State of Charge (SoC) of a battery reflects the ratio of its current charge to its full charge, serving as its “fuel gauge”.
SoC represents the remaining battery capacity in percentage form. For example, 100% SoC means the battery is fully charged, while 0% indicates that the battery has been completely discharged.
SoC can also be represented by voltage level, with higher voltage indicating higher SoC.
Methods for Measuring SoC
1. Coulombic counting
Coulomb counting is a widely used SoC measurement technique. It accurately calculates the battery usage and remaining capacity by calculating the amount of charge flowing in and out during the battery charging and discharging process.
Advantages:
- When the initial SoC is known, the coulomb meter can provide accurate measurement results.
- The monitoring of SoC changes over time is very accurate.
Disadvantages:
- If not properly calibrated, measurement errors will accumulate over time.
- An accurate initial SoC value is required to achieve optimal performance.
- Sensitive to errors and noise during the measurement process.
2. Voltage measurement method
The voltage measurement method estimates the state of charge (SoC) of a battery by detecting its voltage, as it is generally believed that different voltage levels correspond to different SoC values.
This method is favored for its simple operation, but there are some factors that affect accuracy that need to be noted:
Battery type: The relationship between voltage and SoC varies among different types of batteries.
Temperature: Fluctuations in temperature may affect voltage measurements.
Load: The current discharge or charge state of the battery (load condition) will change its voltage.
Advantages:
- The operation is simple and fast.
- No need for complex instruments.
Disadvantages:
- The accuracy is not as good as other SoC measurement methods.
- Easy to be disturbed by various external conditions such as temperature and load.
3. Impedance spectrum
Impedance spectroscopy analysis is a technique for estimating the state of charge (SoC) of a battery by measuring its internal resistance.
This method provides insight into the internal state of the battery by applying a small alternating current (AC) signal to the battery and detecting its voltage response.
Advantages:
- Can provide detailed information about the health status of the battery.
- Under correct operation, it can reflect SoC very accurately.
Disadvantages:
- Professional measuring equipment is required.
- The process is more time-consuming.
- Due to its complexity, it is usually not suitable for daily SoC monitoring.
The necessity of monitoring battery state of charge
State of Charge (SoC) plays a crucial role in preventing battery overcharging and over discharging:
- Monitoring SoC can prevent battery overcharging, which may cause damage to the battery.
- It can also avoid deep discharge of the battery, which can reduce its lifespan.
- Maintaining an appropriate SoC range can extend the battery’s lifespan.
SoC has a significant impact on battery performance and lifespan:
- Ensure that the battery can operate normally.
- Improved the reliability of the battery.
- Helps the battery to perform at its best.
Accurate monitoring of SoC applications:
- Electric vehicles rely on precise SoC readings to avoid running out of battery.
- Accurate SoC monitoring in the field of renewable energy storage helps to efficiently utilize solar and wind energy.
- Portable devices such as smartphones and laptops require accurate SoC monitoring to ensure worry free operation throughout the day.
Part 2: Understanding the battery state of health
Understand battery state of health (SOH)
State of Health (SoH) is an important indicator for measuring the current condition of a battery, reflecting its remaining lifespan.
Battery state of health displays the degree of battery degradation by comparing the current performance of the battery with data from unused new batteries.
For example, if the SoH of a battery is 80%, it means that it can only store 80% of its capacity as a new battery. This indicator is very helpful for determining whether the battery needs to be replaced.
If you use an iPhone, you may have this anxiety: observe the battery health of the phone.
Several methods for evaluating SoH
1. Internal resistance measurement
The measurement of battery internal resistance reveals the health status of the battery:
- Low internal resistance indicates that the battery can efficiently transmit electrical energy.
- High internal resistance means that the battery has difficulty in delivering electrical energy.
- As the battery is used for a longer period of time, its internal resistance will gradually increase.
The methods for measuring internal resistance include:
- Use professional instruments to measure the voltage and current of the battery.
- Apply Ohm’s law to calculate the resistance value (resistance=voltage/current).
- Compare the measurement results with the standard values in the battery specification sheet.
2. Test capacity:
Technological process:
- Firstly, fully charge the battery.
- Then discharge the battery and measure the energy it releases.
- Finally, compare the discharge results with the nominal original capacity of the battery.
Analysis of Capacity Test Results:
If the energy released by the battery is significantly lower than its historical level, it may indicate a better state of health (SoH).
3. Self discharge rate
- Self discharge refers to the phenomenon where a battery naturally loses power without any operation.
- A high self discharge rate usually indicates poor health of the battery.
- On the contrary, a healthy battery should be able to maintain its charge for a long time.
How to measure and interpret self discharge rate:
- Firstly, charge the battery to a fully charged state and then leave it for a week (or a regular period).
- Afterwards, measure the remaining battery level. You can test several times within the cycle and compare the data to obtain more average and accurate values.
- If the battery rapidly loses a significant amount of power during this period, it may indicate poor health.
Key factors affecting battery health status (SoH)
Number of charge and discharge cycles:
Each charging and discharging process will cause certain damage to the battery during use. The more cycles of charge and discharge experienced, the shorter the lifespan of the battery may be.
Working temperature and environmental conditions:
Extreme temperature environments can cause damage to batteries. Stable and suitable temperature conditions are most helpful in maintaining the health of batteries.
Storage conditions and maintenance measures:
Keeping the battery clean and dry is its optimal charging level.
Appropriate storage methods and regular maintenance can extend the lifespan of batteries.
Battery lifespan:
Old batteries usually have decreased performance and reduced storage capacity. If the battery is not used, its performance will gradually decrease over time.
A battery with a lower SoH value means its ability to store charge at a specific voltage decreases, which reduces the practicality of the battery.
By referring to these, important information on battery life expectancy and recommended replacement times can be collected.
Therefore, monitoring SoH is crucial for maintaining battery performance and planning battery replacement.
Part 3: Battery SoH vs SoC
Battery SOH vs SOC:
Battery soc meaning the current remaining charge of the battery.
SoH is the ratio of the current capacity of a battery to its initial capacity (i.e., the capacity of a new battery). Battery soh meaning the information on the overall health status of the battery.
How SoC affects SoH
Overcharging and over discharging that affect battery health:
Overcharging may cause an increase in battery temperature, which can damage the battery in the long run. However, excessive discharge will accelerate the battery’s wear and tear.
Maintain ideal charging state to extend battery life:
Maintaining the state of charge (SoC) of the battery between 20% and 80% can help extend its lifespan, reduce the pressure it bears, and enable it to maintain good working condition for a longer period of time.
How does SoH affect SoC
The impact of battery aging on State of Charge (SoC):
As the battery ages, its storage capacity will gradually decrease, which will affect our accurate judgment of the remaining charge of the battery (SoC). Aging batteries may display incorrect battery readings or rapidly decrease in battery capacity.
SoC estimation for calibrating aged batteries:
In the face of battery aging issues, advanced battery management systems will adjust the measurement methods of SoC.
By considering the internal resistance of the battery and historical usage data, these systems can provide more accurate SoC readings, ensuring accuracy even in the event of battery aging.
The importance of both
The importance of State of Charge (SoC) and State of Health (SoH) in Battery Management Systems (BMS):
SoC increases with the increase of battery voltage and decreases with the discharge of the battery. SoH, the lifespan of the battery gradually decreases with the accumulation of charging and discharging cycles.
Functions of Battery Management System (BMS):
BMS is responsible for monitoring and managing the SoC and SoH of the battery. By continuously tracking these indicators, BMS ensures the safe and efficient operation of batteries, extends their lifespan, and prevents potential failures.
SoC is usually calculated by BMS based on the voltage and current inflow and outflow of the battery. SoH is usually evaluated based on factors such as the number of charge and discharge cycles, service life, and temperature history of the battery.
Ensure safe operation:
BMS ensures the safe operation of batteries by monitoring SoC and SoH. If the SoC is too high or too low, it may cause overcharging or overdischarging, both of which can damage the battery and even pose safety risks such as chemical leaks or fires.
BMS avoids these issues by maintaining SoC within a safe range, ensuring the safe operation of the battery. If the SoH is low, the BMS can alert the user that the battery may need to be replaced.
Extend battery life:
SoC and SoH are crucial for extending battery life. BMS optimizes the charging and discharging process by maintaining SoC within an appropriate range and monitoring SoH, thereby extending the battery’s lifespan.
Optimize energy usage:
Understanding SoH and SoC is equally important for optimizing energy usage. For example, understanding the SoC of electric vehicles can help drivers plan their trips and charging stations.
Similarly, understanding SoC and SoH in home energy storage systems can help optimize energy consumption and reduce electricity bills.
Part 4: The Most Important Considerations for Maintaining SoC and SoH
Routine monitoring:
Please regularly monitor the state of charge (SoC) and health status (SoH) of the battery, and use tools such as the battery management system (BMS) to obtain accurate data.
Track the current status of the battery and make appropriate adjustments.
Temperature control:
Keep the battery in a stable temperature environment and avoid placing it under extreme high or low temperature conditions.
If possible, using a temperature control system would better maintain appropriate SoC and SoH.
Maintenance measures:
Please regularly maintain the battery. Regular maintenance helps ensure that the battery remains in optimal condition and provides good performance.
Check for signs of corrosion or damage. If the health status (SoH) of the battery significantly decreases, it is recommended to replace the battery.
Best practices for charging:
Please avoid overcharging the battery. It is recommended to stop charging when the battery level reaches 80%. Similarly, do not let the battery level drop below 20%.
This helps to reduce the pressure on the battery and extend its lifespan.
Storage suggestion:
Store the battery in a cool and dry place. If not used for a long time, it is recommended to charge the battery to about 50% level and store it, which can help prevent battery performance degradation and maintain the health of the battery.
Conclusion
State of Charge (SoC) and battery state of health (SoH) are core indicators in battery maintenance. By tracking and adjusting these key parameters, ensure the safety, efficiency, and optimal performance of the battery.
Whether you work in a company that produces battery driven equipment, specialize in developing BMS systems, or simply have a passion for battery technology or related needs, mastering the importance of SoC and SoH is essential for battery management.
If you have any interests or questions, you can contact GycxSolar and we can provide solutions and services for you.
