What is self discharge of secondary batteries? What is the self discharge rate of different types of batteries?

Self discharge, also known as charge retention capacity, refers to the ability of a battery to maintain its stored energy under certain environmental conditions in an open circuit state. Generally speaking, self discharge is mainly influenced by manufacturing processes, materials, and storage conditions. Self discharge is one of the main parameters for measuring battery performance.

Generally speaking, the lower the storage temperature of a battery, the lower its self-discharge rate. However, it should also be noted that low or high temperatures may cause damage to the battery and render it unusable.

After the battery is fully charged and left open for a period of time, a certain degree of self discharge is a normal phenomenon. IEC standard stipulates that after fully charged, the Nickel–metal hydride battery shall be kept open for 28 days at a temperature of 20 ± 5 ℃ and a humidity of (65 ± 20)%, and the 0.2C discharge capacity shall reach 60% of the initial capacity.