Open circuit voltage (OCV): When the battery is not discharged, the potential difference between the two poles of the battery is called the open circuit voltage. The open circuit voltage of the battery varies according to the materials of the battery's positive, negative and electrolyte. If the materials of the battery's positive and negative electrodes are exactly the same, the open circuit voltage will be the same no matter how large the battery is or how the geometric structure changes. Over discharge: If the battery exceeds the termination voltage of battery discharge during the discharge process, the internal voltage of the battery may rise when the battery continues to be discharged, and the reversibility of the positive and negative active materials will be damaged, which will damage the battery. The capacity has been significantly reduced. Depth of discharge (DOD): During battery use, the percentage of the battery's rated capacity, which is called the depth of discharge. The depth of discharge has a deep relationship with the charging life of the secondary battery. When the depth of discharge of the secondary battery is deeper, the charging life will be shorter. Therefore, deep discharge should be avoided as much as possible during use. Over charge: When the battery is charged, if it continues to charge after it reaches the full state, it may cause the battery internal pressure to rise, battery deformation, night leakage, etc., and the battery performance will also be significantly reduced and damaged. Energy density: The electric energy released by the average unit volume or mass of the battery. Generally, in the same volume, the energy density of lithium-ion batteries is 2.5 times that of nickel-cadmium batteries and 1.8 times that of nickel-hydrogen batteries. Therefore, when the battery capacity is equal, lithium-ion batteries will be better than nickel-cadmium and nickel-hydrogen batteries. Smaller size and lighter weight. Self discharge: Regardless of whether the battery is used or not, due to various reasons, the battery will lose its power. If calculated in a month, the self-discharge of lithium-ion batteries is about 1%-2%, and the self-discharge of nickel-hydrogen batteries is about 3%-5%. Cycle life: The capacity of the rechargeable battery will gradually decrease to 60%-80% of the initial capacity under repeated use of charging and discharging. Cut-off discharge voltage: Refers to the lowest working voltage value at which the battery discharges when the voltage drops to the battery no longer suitable for discharging. According to different battery types and different discharge conditions, the requirements for the capacity and life of the battery are also different, so the specified terminal voltage of the battery discharge is also different.