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 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 are not designed for recharging between manufacturing and use, and thus to be practical they must have much lower self-discharge rates than older types of secondary cells. Later, secondary cells with similar very low self-discharge rates were developed, like low-self-discharge nickel–metal hydride 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.
| Battery chemistry | Rechargeable | Typical self-discharge or shelf life |
|---|---|---|
| Lithium metal | No | 10 years shelf life[3] |
| Alkaline | No | 5 years shelf life[3] |
| Zinc–carbon | No | 2–3 years shelf life[3] |
| Lithium-ion | Yes | 2–3% per month;[3] ca. 4% p.m.[4] |
| Lithium-polymer | Yes | ~5% per month[5][better source needed] |
| Low self-discharge NiMH | Yes | As low as 0.25% per month[6] |
| Lead–acid | Yes | 4–6% per month[3] |
| Nickel–cadmium | Yes | 15–20% per month[3] |
| Conventional nickel–metal hydride (NiMH) | Yes | 30% per month[3] |