What do DOD, SOC, and SOH mean? Interpretation of core technical parameters of energy storage batteries
Energy storage batteries serve as the cornerstone of the energy storage system, bearing the significant responsibility of providing stable and reliable energy to the system. A thorough understanding of the core technical parameters of energy storage batteries enables us to precisely grasp their performance characteristics and further enhance the overall efficiency of the energy storage system.

1. Battery Capacity (Ah)
Battery capacity is one of the important performance indicators for evaluating the performance of a battery. It represents the amount of electricity discharged by the battery under certain conditions (discharge rate, temperature, termination voltage, etc.). It is usually measured in Ah. Taking a 48V, 100Ah battery cell as an example, the capacity of the battery is 48V × 100Ah = 4800Wh, which is equivalent to 4.8 kilowatt-hours. 
The battery capacity is classified into actual capacity, theoretical capacity and rated capacity under different conditions. The theoretical capacity refers to the capacity of the battery in the most ideal state; the rated capacity is the capacity indicated on the equipment that can be continuously operated for a long time under the rated working conditions; while the actual capacity is affected by factors such as temperature, humidity, and charging-discharging rate, and generally, the actual capacity is smaller than the rated capacity. 

2. Rated Voltage (V)
The rated voltage of an energy storage battery refers to its designed or nominal operating voltage, usually expressed in volts (V). The battery module is composed of individual cells connected in series. By adding more cells in parallel, the capacity increases while the voltage remains the same. When connected in series, the voltage doubles while the capacity remains unchanged. You may come across parameters like 1P24S in the battery PACK specifications: S represents series.

3. Charging and Discharging Rate (C)
The charging and discharging rate of a battery is a measure of how fast it charges. This indicator affects the continuous current and peak current during the battery's operation, and its unit is generally C. Charging and discharging rate = charging and discharging current / rated capacity. For example, if a battery with a rated capacity of 200Ah is discharged at 100A, all the capacity will be discharged in 2 hours, and its discharge rate is 0.5C. In simple terms, the greater the discharge current, the shorter the discharge time. When discussing the scale of an energy storage project, the method of "system maximum power / system capacity" is commonly used for description. For example, a 2.5MW/5MWh commercial and industrial energy storage project. 2.5MW represents the maximum operating power of the system for this project, and 5MWh is the system capacity. If the power of 2.5MW is used for discharging, and it can be fully discharged in 2 hours, then the discharge rate of this project is 0.5C. 

4. Charge and Discharge Depth (DOD)
The discharge depth DOD (Depth of Discharge) is a metric used to measure the percentage of the battery's discharge capacity compared to its rated capacity. Starting from the upper limit voltage of the battery and ending at the lower limit voltage of discharge, all the discharged electricity is defined as 100% DOD. Generally, the deeper the discharge depth, the shorter the battery's cycle life. Battery capacity below 10% may be over-discharged, which can lead to some irreversible chemical reactions that seriously affect the battery's service life. Therefore, in actual project operation, it is important to balance the need for battery operation time and cycle life to achieve the optimal economic and reliability of the energy storage system. 

5. State of Charge (SOC)
The State of Charge (SOC) of a battery is the percentage of the battery's remaining capacity compared to its rated capacity. It is used to indicate the remaining capacity of the battery and represents its ability to continue functioning. When the battery is completely discharged, the SOC is 0; when it is fully charged, the SOC is 1. It is generally expressed as a value between 0 and 100%. 

6. Battery Health Status (SOH)
In simple terms, Battery Health Status (SOH) refers to the ratio of performance parameters to nominal parameters after a battery has been used for a period of time. According to the IEEE (Institute of Electrical and Electronics Engineers) standard, if the capacity of a battery when fully charged is lower than 80% of its rated capacity after being used for a certain period of time, the battery should be replaced. By monitoring the SOH value, the time when the battery reaches its end of life can be predicted, and corresponding maintenance and management can be carried out.