muistivaikutus

The term "muistivaikutus" is a Finnish word that translates to "memory effect" in English. It describes a phenomenon observed in certain types of rechargeable batteries, particularly older nickel-cadmium (NiCd) batteries. The memory effect refers to the tendency of a battery to reduce its maximum usable capacity if it is repeatedly recharged after being only partially discharged.

When a battery experiences the memory effect, it essentially "remembers" the lowest point of discharge it has encountered repeatedly. Consequently, when it is next charged, it may not charge to its full potential, and its voltage may drop prematurely, giving the user the impression that the battery is faulty or has a significantly reduced capacity. This occurs because the electrochemical processes within the battery can form small crystals that impede the flow of ions, effectively creating a false "full" state at a lower charge level.

The memory effect is most pronounced in NiCd batteries. Nickel-metal hydride (NiMH) batteries, which are more common today, are largely immune to this issue. Modern lithium-ion batteries, found in most portable electronics, are also virtually unaffected by the memory effect. To mitigate the memory effect in NiCd batteries, it was often recommended to fully discharge them periodically before recharging. However, with the prevalence of NiMH and lithium-ion technologies, the memory effect is no longer a significant concern for most users.