DALY BMS Explains Battery State of Charge Calculation Methods

DALY BMS, a company specializing in battery technology, has published an article detailing methodologies for calculating a battery's State of Charge (SOC).

SOC, which quantifies the remaining energy in a battery as a percentage of its total capacity, is a crucial parameter for Battery Management Systems (BMS). Accurate SOC estimation is essential for determining remaining energy, managing battery usage, and controlling charging and discharging processes, thereby extending battery lifespan.

The article outlines two primary methods for SOC calculation: the current integration method and the open-circuit voltage (OCV) method. The current integration method calculates SOC by integrating charge and discharge currents over time. It offers simplicity and does not require calibration, but can introduce errors due to internal resistance and other factors.

The OCV method determines SOC by measuring the battery's voltage when there is no load. This approach is straightforward as it avoids current measurement. However, its accuracy depends on the predefined SOC-OCV relationship, which can shift with battery usage and age, necessitating periodic calibration.

DALY BMS highlights that combining both current integration and OCV methods typically yields the most accurate results. In this hybrid approach, current integration tracks charging and discharging, while OCV provides a calibration point. The final SOC is a weighted average of the results from both methods, with coefficients adjusted based on usage and accuracy requirements. The company notes that temperature and internal resistance also influence results, and calibration remains key for reliable SOC determination.