A local school district asked our advice on how best to manage their 2000 lithium-ion laptop computer batteries over summer break, as they have had some failure over past summer breaks.
First, realize that in best conditions lithium-ion cells have a shelf life of only about 3 years. As time goes by, no matter what you do with it, Lithium-ion batteries lose capacity. One way to maintain a fleet of such batteries is to mark the year and month they are replaced, and replace about 1/3 of them every year, to spread maintenance over time.
The best storage conditions for lithium-ion cells is at about 40% of charge in a cool place. Assuming the laptop battery normally lasts about 2 hours, unplugging the PCs when fully charged and letting the laptop auto-power down after 10 to 20 minutes will allow the batteries to be at least partially discharged. If you have a choice of storing them in an air-conditioned space, do so. Heat degrades most batteries.
Lithium-ion cells are slow to discharge (i.e. lose electric charge stored in them). When at mid-capacity, Lithium-ion’s lose about 4% of charge at room temperature. So if they are stored with moderate charge and they are not near end-of-life, they should survive the summer.
Are Lithium ion cells are built with protection circuits that stop the batteries from being overcharged or being completely discharged. It is possible that if a lithium-ion battery is stored when nearly discharged, self-discharge will take the cell voltage so low that the protection will make the battery appear completely dead. This is one of the few cases a lithium-ion battery can be revived with our CADEX Maintenance & Charging Machine.
If the PCs are on desks and plugged in, pragmatically that is no different from what happens to any office bound PC and its battery. While not the ideal method of storage, because they will be topped repeatedly as they self-disharge over time, keeping them plugged is not battery abuse.
Battery Giant of Pittsburgh
10 St. Francis Way, Suite 900
Cranberry Township, PA 16066