• Dagong ESS

What is SOH (State of Health)?

State of Health (SOH) is a core performance indicator used to evaluate the aging condition and remaining capability of a battery compared to its original state when new. SOH is typically expressed as a percentage, representing how much usable capacity, power capability, and efficiency the battery can still deliver.

For example, a battery with 90% SOH can generally provide about 90% of its original capacity and power performance, although the exact relationship may vary depending on application and operating conditions. In modern energy storage systems (ESS), SOH has become a critical metric for safety control, performance assurance, lifecycle management, and investment decision-making.

As energy storage systems are increasingly deployed as long-term infrastructure assets with lifetimes exceeding 10–15 years, accurate SOH monitoring is no longer optional—it is a foundational requirement.

Why Is SOH Important in Energy Storage Systems?

SOH directly affects how reliably and safely an energy storage system can operate over time.

• SOH enables early detection of battery degradation. By identifying abnormal aging trends, operators can take corrective actions before failures occur.

• SOH improves system safety. Aging batteries are more prone to thermal instability, voltage imbalance, and internal resistance growth. Continuous SOH tracking helps prevent unsafe operating conditions.

• SOH supports reliable energy supply. In grid-connected and commercial applications, knowing the true health status of batteries ensures that the system can meet expected power and energy demands.

• SOH plays a vital role in lifecycle-based maintenance and asset valuation, supporting warranty management, financial modeling, and long-term project planning.

Core Technologies for SOH Estimation

Accurate SOH estimation requires a combination of electrochemical understanding, data analytics, and system-level monitoring.

• Capacity Degradation Analysis

By tracking changes in charge and discharge capacity over time, SOH algorithms can estimate how much usable energy the battery has lost due to aging.

• Internal Resistance Monitoring

As batteries age, internal resistance typically increases. Monitoring resistance growth provides valuable insight into power capability degradation and thermal behavior.

• Data-Driven Algorithms and Machine Learning

Modern ESS increasingly rely on data-driven SOH models, using historical operating data, usage patterns, and environmental factors to improve estimation accuracy.

• Electrochemical Impedance Spectroscopy (EIS)

EIS offers deeper insight into internal electrochemical changes and is increasingly used in advanced diagnostics and factory-level analysis.

• BMS-Based Historical Data Integration

SOH estimation combines voltage, current, temperature, SOC, and cycling history collected by the Battery Management System (BMS) to form a comprehensive health assessment.

Challenges of SOH Estimation in Real-World Applications

Despite its importance, SOH estimation remains one of the most challenging aspects of battery management.

One major issue is the lack of standardized SOH calculation methods across the industry. Different manufacturers may define or calculate SOH differently, making comparisons difficult.

Another challenge is accurately capturing aging behavior under partial charge and discharge cycles, which are common in real-world ESS operation but harder to model than full cycles.

Environmental factors such as temperature, humidity, and operating altitude also affect battery aging and introduce uncertainty into SOH estimation.

In addition, different battery chemistries exhibit distinct aging mechanisms, leading to inconsistencies in SOH interpretation.

Finally, real-time SOH visibility at system and module level is still limited in many installations, reducing its practical value for daily operations.

Why Choose Dagong ESS Energy Storage Solutions?

Dagong ESS integrates advanced SOH estimation and monitoring technologies across its entire energy storage product portfolio, enabling smarter operation, safer performance, and longer system life.

• Intelligent SOH Diagnostics

Dagong ESS systems automatically analyze capacity, internal resistance, temperature trends, and cycling behavior to generate accurate and continuously updated SOH assessments.

• Long-Term Performance Tracking

Each battery module is tracked throughout its lifecycle, enabling predictive maintenance, aging trend analysis, and data-driven replacement planning.

• Enhanced Safety Management

SOH data is actively used to prevent operation of excessively aged or abnormal cells, significantly reducing the risk of thermal events and system failures.

• Data Visualization and Reporting

Real-time SOH information is presented through user-friendly dashboards, allowing operators to quickly understand battery condition and system health.

• Compatibility and Customization

Dagong ESS SOH platforms support multiple battery chemistries and can be customized to meet project-specific monitoring, reporting, and integration requirements.

Applications of SOH in Energy Storage Systems

• Predictive Maintenance for C&I Energy Storage

SOH data enables maintenance actions to be scheduled before critical failures occur, minimizing downtime and improving return on investment.

• Grid Reliability and Capacity Planning

For grid-side storage, SOH helps determine whether the system can continue to meet peak shaving, frequency regulation, and reserve capacity requirements.

• Battery Leasing and Second-Life Applications

SOH plays a key role in evaluating used batteries for second-life deployment, supporting sustainability and cost-effective reuse strategies.

Dagong ESS Products Showcase

Dagong ESS incorporates SOH monitoring across all major energy storage product lines:

• Home ESS (5kWh–80kWh)

Designed for residential solar storage with continuous SOH monitoring to ensure long-term battery health.

• Rack-Mounted ESS (30kWh–80kWh)

Modular systems with per-module SOH tracking, suitable for light commercial and backup power applications.

• Air-Cooled C&I Storage Cabinets (100kWh–416kWh)

Industrial-grade solutions featuring SOH analytics for early degradation detection and automated alerts.

• Liquid-Cooled ESS Cabinets (241kWh–5MWh)

Advanced thermal management maintains SOH integrity under high-power cycling and fast charge/discharge conditions.

• Custom Containerized ESS Solutions

Utility-scale systems with centralized SOH management, supporting long-term benchmarking, asset valuation, and investment planning.

Frequently Asked Questions

Q: What does SOH actually indicate?
A: SOH reflects how much a battery has aged and whether it can still deliver sufficient energy and power compared to its original condition.

Q: How often is SOH updated in Dagong ESS systems?
A: SOH is dynamically updated in near real time based on historical data, current operating conditions, and environmental factors.

Q: Is SOH visible to users and operators?
A: Yes. SOH is clearly displayed in web-based dashboards and mobile interfaces alongside other key battery metrics.

Q: What SOH level indicates end of battery life?
A: In most applications, batteries are considered end-of-life when SOH falls below 70–80%, depending on system requirements.

Q: Does Dagong ESS support SOH evaluation for second-life use?
A: Yes. Dagong ESS systems can assess remaining battery value and suitability for secondary, lower-demand applications.