Self-discharge

Self-discharge is a phenomenon in batteries in which internal chemical reactions reduce the stored charge of the battery without any connection between the electrodes or any external circuit.[1] Self-discharge decreases the shelf life of batteries and causes them to initially have less than a full charge when actually put to use.[1]

How fast self-discharge in a battery occurs is dependent on the type of battery, state of charge, charging current, ambient temperature and other factors.[2] Primary batteries aren't designed for recharging between manufacturing and use, thus have battery chemistry that has to have a much lower self-discharge rate than older types of Secondary cells, but they have lost that advantage with the development of rechargeable Secondary Cells with very low self discharge rates like Low Self Discharge NiMH cells.

Self-discharge is a chemical reaction, just as closed-circuit discharge is, and tends to occur more quickly at higher temperatures. Storing batteries at lower temperatures thus reduces the rate of self-discharge and preserves the initial energy stored in the battery. Self-discharge is also thought to be reduced as a passivation layer develops on the electrodes over time.