Battery balancing is a critical function in modern lithium battery systems, especially for LiFePO4 batteries used in energy storage applications. By maintaining consistent voltage levels between individual battery cells, balancing helps improve battery safety, optimize usable capacity, and support stable BMS operation.
In a battery pack, small differences between cells can gradually affect charging efficiency and discharge performance. Understanding how battery balancing works allows engineers and energy storage users to better evaluate battery reliability and system performance.
What is Balancing?
Balancing is equalizing the voltage of individual cells in a battery system. It means bringing each cell’s voltage closer to the pack’s average voltage.
Why is Balancing Necessary?
In battery systems, cells are often connected in series to achieve higher voltage levels that meet the load requirements. For example, a battery pack consists of 16 individual cells in series. Cell internal resistance will differ due to the manufacturing date, environment, electrode thickness, and electrolyte volume.
According to Ohm’s Law, differences in internal resistance lead to differences in cell voltages. In a series circuit, the current is constant throughout the circuit during charging and discharging. Cells with higher internal resistance will reach their voltage limit value sooner during charging and drop to their voltage limit value faster during discharging. This phenomenon represents the inconsistency within a battery system.
Such inconsistencies can cause irreversible damage to the battery pack or even catastrophic failure. Therefore, balancing is essential to ensure cell voltages approach or within safe upper limits, thus safeguarding the battery system’s operation.
Benefits of Balancing
One of the primary purposes of balancing is to enhance the safety of the battery system. Additionally, balancing can improve the system’s usable capacity.
How does balancing increase usable capacity?
Without balancing, when one cell in a pack reaches its upper voltage limit during charging, the monitoring circuit signals the control system to stop charging, leaving the pack undercharged.
With balancing, the Battery Management System (BMS) continuously monitors voltage differences and upper voltage limits. Once the preset voltage difference is reached, the balancing function activates. The balancer regulates the charging current for individual cells, reducing charging for cells with higher voltages and increasing it for those with lower voltages. This mechanism extends the charging time and increases the system’s chargeable capacity, thus improving its usable capacity.
From a State of Charge (SOC) perspective, without balancing, the SOC range is typically limited to 20% to 80% for safety reasons, providing only 60% usable capacity. With balancing, the SOC range can be expanded from 5% to 95%, increasing usable capacity to 90%. This means the battery pack’s usable capacity is significantly enhanced.
Therefore, balancing improves the Depth of Discharge (DOD), making the battery system more efficient.
It’s important to note that balancing only equalizes cell voltages to the average value of the pack and does not alter the inherent characteristics of the cells. Can balancing slow down cell degradation? There is no conclusive data in the industry to confirm this, and further research is needed.
Additionally, many BMS manufacturers are pushing to increase balancing currents, to improve balancing efficiency. However, even large balancing currents cannot save low-quality cells. Overstating the role of balancing is incorrect and irresponsible to consumers.
The True Role of Balancing
Battery balancing is an essential function for maintaining safe and efficient battery operation. While balancing cannot change the characteristics of individual cells, it helps reduce voltage differences, improve usable capacity, and support more reliable battery system performance.
For energy storage applications, choosing a battery system with an intelligent BMS and reliable balancing technology is essential. Seplos integrates advanced BMS solutions into its lithium battery systems to provide safer and more efficient energy storage solutions.
Explore Seplos battery solutions and discover how advanced battery management technology can support your energy storage projects.
FAQ About Battery Balancing
How does battery balancing work in a BMS?
A Battery Management System (BMS) monitors individual cell voltages and activates balancing functions when voltage differences exceed preset limits, helping maintain a more balanced battery pack.
What happens if a battery pack has cell voltage differences?
Large cell voltage differences can reduce usable capacity, cause uneven charging and discharging, and may affect the overall safety and performance of the battery system.
What is the difference between active and passive battery balancing?
Passive balancing removes excess energy from higher-voltage cells through resistors, while active balancing transfers energy between cells to improve efficiency.
Can higher balancing current fix poor-quality battery cells?
No. Higher balancing current cannot compensate for low-quality cells. Balancing only reduces cell differences and cannot change the fundamental characteristics of battery materials.
Is battery balancing important for energy storage systems?
Yes. Battery balancing plays an important role in maintaining safe operation, improving usable capacity, and ensuring reliable performance of energy storage systems.
