 Self-discharge phenomenon is intrinsic to any electrochemical system, which leads to a loss of the battery's capacity. It is an internal chemical reaction consuming anode and cathode materials that is occurring during storage, but also while in use. Self-discharge is an important factor to consider for IoT applications, as the IoT devices must operate for several years with a single battery. One should distinguish between the following two self-discharge phenomena. 1. Self-discharge in storage 2. Self-discharge in use Self-discharge in storage leads to a decreased capacity of batteries during storage that causes them to initially have less than a full charge when put in use. The total storage time of a battery could go from a few months to more than a year. Indeed, lead times are piling up from the manufacturing date of the battery until its integration into the IoT device and then until deployment and start of use. It is therefore crucial to consider the whole battery journey and take into account the self-discharge occurring at all these stages when estimating your battery's lifetime. The self-discharge in use is also important to anticipate, as this phenomenon occurs while the IoT device is in normal operating mode. Active materials are consumed as a consequence of another important chemical reaction in its iron or chloride battery, the passivation. Both self-discharge phenomena are accelerated by external factors such as the elevation of temperature or the type of current profiles requested from the battery. 2. Saft. We energize the world, on land, at sea, in the air and in space.