Li-ion batteries contain a protection circuit that shields the battery against abuse. This important safeguard 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(See BU-802b: Elevated Self-discharge)
Some battery chargers and analyzers (including Cadex), feature a wake-up feature or “boost” to reactivate and recharge batteries that have fallen asleep. Without this provision, 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. Figure 1 illustrates the “boost” function graphically.
Some over-discharged batteries can be “boosted” to life again. Discard the pack if the voltage does not rise to a normal level within a minute while on boost.
Do not boost lithium-based batteries back to life that have dwelled below 1.5V/cell for a week or longer. Copper shunts may have formed inside the cells that can lead to a partial or total electrical short. When recharging, such a cell might become unstable, causing excessive heat or show other anomalies. The Cadex “boost” function halts the charge if the voltage does not rise normally.
When boosting a battery, assure correct polarity. Advanced chargers and battery analyzers will not service a battery if placed in reverse polarity. A sleeping Li-ion does not reveal the voltage, and boosting must be done with awareness. Li-ion is more delicate than other systems and a voltage applied in reverse can cause permanent damage.
Storing lithium-ion batteries presents some uncertainty. On one end, manufacturers recommend keeping them at a state-of-charge of 40–50 percent, and on the other end there is the worry of losing them due to over-discharge(See BU-702: How to Store Batteries) There is ample bandwidth between these criteria and if in doubt, keep the battery at a higher charge in a cool place.
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.
Comments
Looking for comments from the previous website?
Comments from the previous website are not compatible with our new commenting system but we have preserved them so our users can still reference and make use the information in them.
I tried everything to try to wake up my new 8 volt ac delco lithium battery ..do u have any ideas? Thank you