If a cell's voltage reaches a designed value, that means the battery has discharge the stored capacity, but still the discharge action is continual, over-discharge will cause. Commonly the end voltage can be identified through discharge current, for example the end voltage is set at 1.0V/cell as discharged at 0.2C-2C, and 0.8V/cell at 3C or more, e.g. 5C or 10C. Over discharge may cause disaster, especially at heavy current or repeated over discharge. Commonly over discharge can make cell inner pressure raise, and the reversibility of activity materials both in positive and negative will be damaged. Even by charge only part can recover and the capacity is reduced obviously.