The state of charge can be defined as the state of available electrical energy in the battery, usually expressed as a percentage. Because the available energy will vary depending on the charging and discharging current, temperature, and aging phenomenon, the definition Of the State of Charge is also divided into two types: Absolute state-of-charge; ASOC) and Relative State-Of-Charge; RSOC). Usually the range of relative charged state is 0% – 100%, while the battery is 100% when fully charged and 0% when fully discharged. The absolute state of charge is a reference value calculated from the designed fixed capacity value when the battery is manufactured. The absolute state of charge of a new fully rechargeable battery is 100%; Even if the aging battery is fully charged, it can not reach 100% in different charging and discharging conditions.
The following figure shows the relationship between voltage and battery capacity at different discharge rates. The higher the discharge rate, the lower the battery capacity. When the temperature is low, the battery capacity also decreases
FIG. 1. Relationship between voltage and capacity at different discharge rates and temperatures
Battery capacity detection data is related to the characteristics of the battery itself, charging and discharging conditions, and the accuracy of the detection instrument itself. Each detection data of the same battery is not exactly the same, usually the same detection step is set when the battery capacity is detected, and the cycle test is conducted until the battery data is basically stable. Usually set 0.5C for charge and discharge test battery capacity, the test environment to maintain ventilation and heat dissipation, conditions can be carried out in the environment of air-conditioned room, the battery itself is heated when testing, reducing the external temperature can ensure the equipment life, reduce the maintenance rate and replacement rate, to ensure the continuous operation of the equipment.
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