BU Summarized: How to Awaken a Sleeping Li-ion

November 07, 2017

One of the most popular recent articles on the Cadex sponsored educational website BatteryUniversity.com presents a detailed look at what causes Li-ion batteries to fall asleep and how to keep them awake. Here, on the Cadex blog, we've condensed the article and presented the key points. After reading this if you want to learn more, please click here.

How to Awaken a Sleeping Li-ion

Learn what you can do to prevent a Li-ion battery from falling asleep.

Li-ion batteries contain a protection circuit that shields the battery against abuse, which also turns the battery off and makes it unusable if over-discharged. Slipping into sleep mode can happen when storing a Li-ion pack in a discharged state for any length of time as self-discharge would gradually deplete the remaining charge. Depending on the manufacturer, the protection circuit of a Li-ion cuts off between 2.2 and 2.9V/cell.

Some battery chargers and analyzers (including Cadex analyzers), feature a wake-up feature or “boost” to reactivate and recharge batteries that have fallen asleep. Without this feature, a charger renders these batteries unserviceable and the packs would be discarded. Boost applies a small charge current to activate the protection circuit and if a correct cell voltage can be reached, the charger starts a normal charge. 

When storing lithium-ion batteries, manufacturers recommend keeping them at a state-of-charge of 40–50 percent. If in doubt, keep the battery at a higher charge in a cool place.

Case Study:
Cadex examined 294 mobile phones batteries that were returned under warranty. The Cadex analyzer restored 91 percent to a capacity of 80 percent and higher; 30 percent were inactive and needed a boost, and 9 percent were non-serviceable. All restored packs were returned to service and performed flawlessly. This study shows the large number of mobile phone batteries that fail due to over-discharging and can be salvaged.

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