Self-discharge is a phenomenon in batteriesBook: Encyclopedia of Electrochemical Power Sources. Garche. Jurgen. Dyer. Chris K.. Moseley. Patrick T.. Ogumi. Zempachi. Rand. David A. J.. Scrosati. Bruno. 2013. Newnes. 978-0-444-52745-5. 407. 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 | |
|---|---|---|---|
| No | 10 years shelf life | ||
| No | 5 years shelf life | ||
| No | 2–3 years shelf life | ||
| Yes | 2–3% per month; ca. 4% p.m.[3] | ||
| Yes | ~5% per month[4] | ||
| Yes | As low as 0.25% per month[5] | ||
| Yes | 4–6% per month | ||
| Yes | 15–20% per month | ||
| Conventional nickel–metal hydride (NiMH) | Yes | 30% per month |