Like all types of batteries, lithium-ion batteries also exhibit unavoidable self-discharge. This type of discharge depends primarily on the temperature but also on the charge status and age of the battery. Over extended periods, or even due to excessively long storage of a battery not charged sufficiently beforehand, there is a risk of the cell voltage dropping below a required minimum value. This is called deep discharge and generally leads to irreversible damage to the cells and thus to a total failure of the battery. Even a modern battery management system (BMS) is not capable of preventing this issue. In practice it is recommended to store a lithium-ion battery with a charge status of approx. 40–60 % in a dry and cool (15–20 °C) place depending on the length of planned storage (often over the winter). If being stored for longer, the charge status should be checked every 4–8 weeks and recharged, if necessary.