Charge cycle
{{Short description|Charging and discharging a battery}}
A charge cycle is the process of charging a rechargeable battery and discharging it as required into a load. The term is typically used to specify a battery's expected life, as the number of charge cycles affects life more than the mere passage of time. Discharging the battery fully before recharging may be called "deep discharge"; partially discharging then recharging may be called "shallow discharge".
A "charge cycle" is not a unit of time; the length of time spent charging or discharging does not affect the number of charge cycles.{{Cite journal|title=Degradation of Commercial Lithium-Ion Cells as a Function of Chemistry and Cycling Conditions|date=1 August 2022|doi=10.1149/1945-7111/abae37 |last1=Preger |first1=Yuliya |last2=Barkholtz |first2=Heather M. |last3=Fresquez |first3=Armando |last4=Campbell |first4=Daniel L. |last5=Juba |first5=Benjamin W. |last6=Romàn-Kustas |first6=Jessica |last7=Ferreira |first7=Summer R. |last8=Chalamala |first8=Babu |journal=Journal of the Electrochemical Society |volume=167 |issue=12 |page=120532 |s2cid=225506214 |doi-access=free }}
Each battery is affected differently by charge cycles.{{Cite web|url=https://www.osti.gov/servlets/purl/1474853|title=Understanding the Trilemma of Fast Charging, Energy Density and Cycle Life of Lithium-ion Batteries|date=1 August 2022}}{{Cite web|url=https://mytravel-magazin.de/produkte/beste-powerstation-test/|title=Powerstation im Test|date=1 August 2022|language=de}}
In general, number of cycles for a rechargeable battery (the cycle life) indicates how many times it can undergo the process of complete charging and discharging until failure or starting to lose capacity.{{cite book|author=Tony Bove|title=iPod & iTunes For Dummies, Book + DVD Bundle|url=https://books.google.com/books?id=hASIU1Z3HVAC&pg=PA26|accessdate=19 June 2013|date=2 February 2010|publisher=John Wiley & Sons|isbn=978-0-470-59070-6|pages=26}}{{cite book|author=G. S. George|title=Applied Science II|date=1 January 2007|publisher=Technical Publications|isbn=978-81-8431-146-4|page=8}}{{cite book|author=United Nations|title=Recommendations on the Transport of Dangerous Goods: Manual of Tests and Criteria|year=2009|publisher=United Nations Publications|isbn=978-92-1-139135-0|page=394}}{{cite book|author=Davide Andrea|title=Battery Management Systems for Large Lithium Ion Battery Packs|url=https://books.google.com/books?id=o-QpFOR0PTcC&pg=PA189|accessdate=19 June 2013|year=2010|publisher=Artech House|isbn=978-1-60807-105-0|pages=189}}
Apple Inc. clarifies that a charge cycle means using all the battery's capacity, but not necessarily by discharging it from 100% to 0%: "You complete one charge cycle when you’ve used (discharged) an amount that equals 100% of your battery’s capacity — but not necessarily all from one charge. For instance, you might use 75% of your battery’s capacity one day, then recharge it fully overnight. If you use 25% the next day, you will have discharged a total of 100%, and the two days will add up to one charge cycle."[https://www.apple.com/batteries/why-lithium-ion/ Batteries - Why Lithium-ion? - Apple]