What is Battery SOF and How to Estimate it?

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What is battery sof and how to estimate it

Batteries power our modern world, fueling everything from our smartphones to electric vehicles and renewable energy storage systems. However, behind the convenience of these energy sources lies a complex landscape of variables that directly impact their performance and longevity. One crucial aspect that governs a battery’s operational health is its “State of Function” (battery SOF).

But what exactly is SOF, and why does it matter?

In this exploration of batteries and their inner workings, we will delve into the concept of the State of Function, unraveling the mysteries that shroud this crucial metric. As we navigate through the intricacies of battery technology, we will not only define and dissect SOF but also discover how it influences the lifespan, efficiency, and overall performance of batteries in diverse applications.

We will demystify the enigmatic State of Function, empowering you with insights into the heartbeat of your batteries and providing valuable knowledge on estimating and optimizing their operational status. Whether you’re a tech enthusiast, a conscientious consumer, or an industry professional, understanding SOF is key to unlocking the full potential of the batteries that power our daily lives.

What is Battery SOF?

The State of Function (SOF) of a battery encapsulates its current condition, reflecting how well it can fulfill its intended purpose. Think of it as a health indicator for batteries. This metric takes into account various internal and external factors that influence a battery’s performance, efficiency, and overall functionality.

Battery SOF is based on the current state of the battery over a period of time and predicts the maximum power capability of the battery when charging and discharging any composite without exceeding the battery’s given battery limit conditions. The limit conditions include voltage limit, soc limit, power limit, and current limit. The battery SOF provides power information for the vehicle to meet the acceleration and hill climbing, regenerative braking, and feeds the above information back to the vehicle controller. So the battery SOF is an important parameter for the state estimation of the battery management system.

Factors that Influence State of Function

To grasp the nuances of the State of Function, it’s essential to explore the factors that contribute to its fluctuations.

Factors that influence sof

Internal Factors

  • Chemical Changes: Batteries are intricate electrochemical systems where energy is stored and released through a series of chemical reactions. As time elapses, these reactions cause subtle changes in the battery’s chemistry. This evolution is a natural consequence of the electrochemical processes occurring within the battery. Over repeated charge and discharge cycles, chemical components may undergo transformations, leading to the formation of by-products or the degradation of active materials.As chemical alterations progress, the efficiency of energy storage and release can be compromised, influencing factors such as capacity and voltage. Monitoring and managing these internal chemical dynamics are pivotal in sustaining optimal SOF over the lifespan of the battery.
  • Structural Integrity: The physical structure of a battery, encompassing electrodes, separators, and other internal elements, forms the backbone of its overall health. Any compromise in structural integrity can have a cascading effect on the battery’s performance. For instance, electrode materials may degrade or form undesirable deposits over time, affecting the efficiency of energy transfer. Separators, responsible for preventing short circuits between electrodes, can deteriorate, compromising the safety and longevity of the battery. A holistic assessment of structural integrity provides insights into the robustness of a battery’s architecture and its ability to endure the rigors of daily use.

External Factors

  • Temperature: Extreme temperatures, be they scorching heat or freezing cold, can disrupt the delicate balance within a battery. High temperatures accelerate chemical reactions, hastening the aging process and leading to a decline in SOF. On the flip side, frigid temperatures can slow down chemical reactions, impeding the battery’s ability to deliver power promptly.
  • Charge/Discharge Cycles: The life story of a battery is written in the cycles of charge and discharge it undergoes. Each cycle contributes to the wear and tear experienced by the battery. The more cycles a battery completes, the more pronounced the impact on its long-term State of Function.¬†This phenomenon is particularly relevant in rechargeable batteries powering devices from smartphones to renewable energy storage systems. Being mindful of the number of charge/discharge cycles a battery undergoes helps users gauge its remaining lifespan and make informed decisions about usage patterns and maintenance practices.

How to Estimate Battery SOF

Estimating the SOF of a battery can simply be thought of as estimating the maximum available power of the battery. Generally speaking, the maximum available power of a battery is limited by parameters such as current, voltage, SOC, temperature, etc., and is also related to the aging degree and fault state of the battery. Following is the battery SOF formula:

SOF formula

where P is the power provided by the battery, P_demands is the power demand, and Pmax is the maximum deliverable power (under ideal SOC, SOH, and temperature conditions). While state of charge (SOC) indicates the present charge level and state of health (SOH) reflects lifetime degradation, SOF directly quantifies functional performance accounting for current SOC, SOH, temperature limitations, and other factors. The SOF metric effectively characterizes usable power under real-world operating scenarios.

Commonly used SOF estimation methods can be divided into two categories: methods based on battery MAP diagrams and dynamic methods based on battery models.

1) Based on MAP Graph Algorithm

Based on the battery test (usually HPPC test) data and the maximum and minimum voltage limits, the maximum charging and discharging power under different SOC can be obtained. Battery testing at different temperatures and different levels of attenuation can establish the relationship between the maximum charging and discharging power and temperature, SOC, SOH, and obtain the maximum charging and discharging power MAP diagram. Based on the MAP diagram, the real-vehicle BMS can interpolate to obtain the maximum charging and discharging power of the battery and realize the SOF estimation.

BMS state

Do et al. investigated the maximum charging and discharging power under different SOC, temperature, and cumulative discharge capacity, and established the functional analytical equation of the maximum charging and discharging power to realize the prediction of SOF. The estimation method based on MAP diagrams is simple and direct, but it needs to store multi-dimensional MAP diagrams and only considers the static characteristics, while there are some limitations for the estimation of charging and discharging power under dynamic operating conditions.

2) Dynamic Algorithm Based on Battery Model

According to the battery model, the maximum charging and discharging current can be obtained by considering the current, voltage, SOC, power, and other limitations of the battery, so as to calculate the maximum charging and discharging power of the battery. According to the battery model, the terminal voltage of the battery under different current input cases is given. Through iterative calculation, the maximum current Imax, voltage, and the minimum current Imin, voltage allowed by the battery monomer under the voltage limitation conditions are obtained. The maximum and minimum currents under the limitation of the battery side reaction rate are considered from the mechanism of the battery, which is similar to the method of obtaining the maximum charging and discharging currents under the limitation of the terminal voltage. Finally, the above limitations are considered together to obtain the maximum and minimum current of the battery monomer. The multi-parameter estimation method based on the dynamic model is essentially a voltage limitation method based on the Thevenin model, which synthesizes the SOC and current limitations, and then obtains the maximum charging and discharging current.


The State of Function is the pulse of a battery, dictating its efficiency, capacity, and overall performance. Whether you’re powering your smartphone, navigating in an electric vehicle, or relying on renewable energy storage, the SOF of your batteries plays a pivotal role in your daily experiences.
As we conclude this exploration, it’s crucial to acknowledge the role of innovative solutions and reliable partners in optimizing battery performance. One such player in the field is MOKOEnergy, a professional Battery Management System (BMS) OEM & ODM service provider.
At MOKOEnergy, our mission is to enable the full potential of batteries through smart battery management. With seasoned expertise, customizable technology, and an unrelenting focus on quality, we empower batteries to operate safely, efficiently, and reliably over long lifetimes. Our BMS solutions uniquely quantify real-time battery capability, helping extract every ounce of usable power. By partnering with MOKOEnergy, companies can bring robust, high-performing battery systems to market faster. With superior battery management technology backed by a commitment to service, we strive to accelerate the future of energy storage. Choose MOKOEnergy for capable, long-lasting batteries that are ready for the challenges of tomorrow.

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