selfdischarging

Selfdischarging, commonly referred to as self-discharge, is the gradual loss of stored electrical energy in a battery when it is not connected to a load or external circuit. It results from intrinsic chemical reactions within the cell and, in some designs, from minor leakage paths or gas formation. This process reduces the available capacity even when the battery is idle.

Mechanism wise, even at rest electrodes and electrolytes interact slightly; impurities and side reactions consume active materials, increase internal resistance, and lower usable capacity. The rate depends on the cell chemistry, construction, and temperature. Temperature accelerates these reactions, so storage at higher temperatures speeds self-discharge.

Self-discharge rates vary by chemistry. Lithium-based cells (such as lithium-ion) typically lose a small fraction of capacity each month—often a few percent—with higher rates at elevated temperatures. Nickel-based chemistries (NiMH, NiCd) generally exhibit higher self-discharge, though modern low-self-discharge NiMH varieties are better than older types. Lead-acid batteries also self-discharge at modest rates, and storage conditions such as high temperature can increase the loss. In practice, real-world rates vary widely with design, manufacturing quality, and age.

Factors influencing self-discharge include storage temperature, state of charge at rest, age, and number of cycles. Higher temperatures increase the rate, while cooler storage helps. For lithium-ion batteries, storage at a partial state of charge, typically around 40–60%, and in a cool environment can reduce self-discharge losses. Age and history of use also affect how fast a battery self-discharges.

Mitigation revolves around proper storage and handling. Follow manufacturer guidance for storage voltage and conditions, keep batteries in a cool, dry place, and use battery management systems for packs. For long-term storage, periodic recharging may be advised to prevent deep discharge in certain chemistries.