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. Self-discharge decreases the shelf-life of batteries and causes them to initially have less than a full charge when actually put to use.

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. Typically, among rechargeable batteries, 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), with the exception of Low self-discharge NiMH batteries (2-3% per month).

Primary batteries, which cannot be recharged between manufacturing and use, have much lower self-discharge rates.

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 passivation layer develops on the electrodes.

The detailed chemical causes of self-discharge depend on the particular battery and are not well understood.

References

• Battery performance characteristics, MPower UK, 23 February 2007. Information on self-discharge characteristics of battery types
• Wu and White, "Self-Discharge Model of a Nickel-Hydrogen Cell." Journal of the Electrochemical Society, 147 (3) 901-909 (2000).

External links

• Battery dischargers Description and treatment of sulphated batteries