Memory effect: Difference between revisions
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===Permanent loss of capacity=== |
===Permanent loss of capacity=== |
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====Deep discharge==== |
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Some rechargeable batteries can be damaged by repeated deep discharge. Batteries are composed of multiple similar, but not identical, cells. Each cell has its own charge capacity. As the battery as a whole is being deeply discharged, the cell with the smallest capacity may reach zero charge and will "reverse charge" as the other cells continue to force current through it. The resulting loss of capacity is often ascribed to the memory effect. |
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Battery users may attempt to avoid the memory effect proper by fully discharging their battery packs. This practice is likely to cause more damage as one of the cells will be deep discharged. The damage is focused on the weakest cell, so that each additional full discharge will cause more and more damage to that cell. |
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====Age and use—normal end-of-life==== |
====Age and use—normal end-of-life==== |
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Revision as of 05:31, 17 July 2015
 | This article needs additional citations for verification. (January 2007) |
Memory effect, also known as battery effect, lazy battery effect or battery memory, is an effect observed in nickel cadmium and nickel–metal hydride rechargeable batteries that causes them to hold less charge.[1] It describes the specific situation in which certain NiCd and NiMH batteries gradually lose their maximum energy capacity if they are repeatedly recharged after being only partially discharged. The battery appears to "remember" the smaller capacity.[2] The source of the effect are changes in the characteristics of the underused active materials of the cell.[citation needed] The term is commonly misapplied to almost any case in which a battery appears to hold less charge than was expected. These cases are more likely due to battery age and use, leading to irreversible changes in the cells due to internal short-circuits, loss of electrolyte, or reversal of cells.
Other problems perceived as memory effect
Phenomena which are not true memory effects may also occur in other battery types than sintered-plate nickel-cadmium cells.
Temporary effects
Voltage depression due to long-term over-charging
A common process often ascribed to memory effect is voltage depression. In this case the peak voltage of the battery drops more quickly than normal as it is used, even though the total energy remains almost the same. In modern electronic equipment that monitors the voltage to indicate battery charge, the battery appears to be draining very quickly. To the user it appears the battery is not holding its full charge, which seems similar to memory effect. This is a common problem with high-load devices such as digital cameras.
Voltage depression is caused by repeated over-charging of a battery, which causes the formation of small crystals of electrolyte on the plates. These can clog the plates, increasing resistance and lowering the voltage of some individual cells in the battery. This causes the battery as a whole to seem to discharge rapidly as those individual cells discharge quickly and the voltage of the battery as a whole suddenly falls. This effect is very common, as consumer trickle chargers typically overcharge.
- Repair
The effect can be overcome by subjecting each cell of the battery to one or more deep charge/discharge cycles.[3] This must be done to the individual cells, not a multi-cell battery; in a battery some cells may discharge before others, they are then subjected to a reverse charging current by the remaining cells, causing irreversible damage.
High temperatures
High temperatures reduce the charge accepted by the cells and the voltage charged to.[4]
Other causes
- Operation below 0 °C (32 °F)
- High discharge rates (above 5C) in a battery not specifically designed for such use
- Inadequate charging time
- Defective charger[4]
Permanent loss of capacity
Age and use—normal end-of-life
All rechargeable batteries have a finite lifespan and will slowly lose storage capacity as they age due to secondary chemical reactions within the battery whether it is used or not. Some cells may fail sooner than others, but the effect is to reduce the voltage of the battery. Lithium-based batteries have one of the longest idle lives of any construction, and examples abound that are nearly 20 years old which exhibit almost their as-new capacity[citation needed]. Unfortunately the number of operational cycles is still quite short at approximately 400-1200 complete charge/discharge cycles.[5] The lifetime of lithium batteries decreases at higher temperature and states of charge (SoC), whether used or not; maximum life of lithium cells when not in use(storage) is achieved by refrigerating (without freezing) charged to 30%-50% SoC. To prevent overdischarge battery should be recharged to 50% SoC once every six months or once per year[6][7]
References
- ^ Bergveld, H.J.; Kruijt, W.S.; Notten, Peter H. L. (2002-09-30). Battery Management Systems: Design by Modelling. Springer. pp. 38–. ISBN 9781402008320. Retrieved 5 June 2013.
- ^ David Linden, Thomas B. Reddy (ed). Handbook Of Batteries 3rd Edition. McGraw-Hill, New York, 2002 ISBN 0-07-135978-8 page 28-18
- ^ Batteries as sources of electrical power
- ^ a b Cite error: The named reference
GEnotewas invoked but never defined (see the help page). - ^ Battery Types and Characteristics for HEV ThermoAnalytics, Inc., 2007. Retrieved 2010-06-11.
- ^ "Lithium-Ion Battery Maintenance ZZZ Guidelines" (PDF). Tektronix, Inc. Retrieved 16 December 2013.
- ^ "Lithium-Ion & Lithium Polymer Cells and Batteries Safety Precautions". Ultralife corporation. Retrieved 16 December 2013.
Sources
- Rechargeable Batteries Applications Handbook from Gates Energy Products, published since 1992 April 10.