Rated capacity refers to the minimum amount of electricity that the battery should discharge under certain discharge conditions when designing and manufacturing batteries, and is often referred to as the nominal capacity. It is worth noting that the capacity of a battery is determined by the capacity of one of the electrodes, not the sum of the capacities of the positive and negative electrodes. Therefore, the actual battery capacity is determined by the electrode with the smaller capacity. Generally, the negative electrode capacity is excessive in actual production, and the positive electrode capacity limits the capacity of the entire battery. This is what everyone needs to know before understanding how to measure the battery capacity of an electric vehicle.
The battery capacity measurement method is basically the same as the battery discharge performance detection method, including constant current discharge method, constant resistance discharge method, constant voltage discharge method, constant voltage and constant current discharge method, continuous discharge method and intermittent discharge method. The capacity of the battery can be calculated according to the discharge time and the magnitude of the current. The following mainly introduces the constant current discharge method: The discharge capacity of the galvanostatic method has a great relationship with the discharge current, and the discharge temperature, charging system, and shelving time will all affect the capacity. Under the same discharge regime, different charging regimes have inconsistent charging efficiency for the battery, so the discharge capacity of the battery will also be different. Similarly, under the same charging system, the discharge capacity test after 10 minutes and 1 hour of storage will result in a difference of 2% to 5%, depending on the self-discharge performance of the battery.
During the discharge process of the constant resistance method to test the capacity, the discharge current is not a constant value. The discharge starts with a larger current and then gradually becomes smaller. The larger the discharge resistance, the smaller the discharge current, the smaller the voltage drop, the slower the working voltage, the flatter the discharge curve, and the larger the discharge capacity.