Self-discharge

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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. Self-discharge decreases the shelf-life of batteries and causes them to have less charge than expected when actually put to use.
How fast self-discharge in a battery occurs is dependent on the type of battery. Typically, lithium batteries suffer the least amount of self-discharge (around 2-3% discharge per month), while nickel-based batteries are more seriously affected by the phenomenon (nickel cadmium, 15-20% per month; nickel metal hydride, 30% per month).
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 over time as a passivity film develops on the electrodes.
The detailed chemical causes of self-discharge depend on the particular battery and are not well understood.




There has also been a discussion on this forum about storing batteries in the refrigerator to slow self discharge. There have been some difference of opinion with each side linking articles to support their position.

IMHO the self discharge rate of lithium batteries is so low it is hardly a concern. If you don't use them in six months, just put them in the charger and top them off. NMh and NiCad on the other hand have a much higher discharge rate and should be recharged every two to three months. (if i were using for my bike, i would make sure they were fully charged before heading out)