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How do you revive a dead li-ion battery?

  • bernards Tuesday, June 02, 2009 1:51 AM Reply
    I have a few blue unprotected Ultrafire li-ion batteries drop to about 1v. Anybody know how do I revive them again?
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  • tom19 Tuesday, June 02, 2009 1:57 AM Reply
    Try charging them for about ten minutes using another good and fully charged lithium ion battery of the same type and voltage. Connect the two in parallel. Then charge the dead batteries using your charger.

    I have tried this and I was able to revive 2 cells.
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  • Nisei Tuesday, June 02, 2009 2:22 AM Reply
    1V? Then they're certainly damaged now. Be careful with them.
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  • Ghlargh Tuesday, June 02, 2009 8:08 AM Reply
    Do NOT try to parallel connect with a full voltage cell, this could make them explode... This is only somewhat safe for protected cells.

    The way to revive a low voltage cell is to charge with a very low voltage over extremely long time, say 5mA.

    All good LiIon chargers will have this function. You might have to restart the chargers from time to time if they have a function that times out if the charging goes on for too long.

    If you do not have a good charger, you can hook the battery in parallel with a full cell, but with a large resistor between them so the current is kept very low, say 500 ohms. for example, connect minus poles together, then connect plus poles to each end of a resistor, then leave like this for several hours).

    The revived cell might work, but might be damaged. Most usual damage is that the cell can no longer supply full current.
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  • Kleinalrik Tuesday, June 02, 2009 11:49 AM Reply
    What works often:
    Shock the battery with a higher voltage. This means, connect the contacts with a higher voltage for but only a few seconds (important).

    The charging voltage should be 30 to 50% higher than the cell´s voltage (i.e. for one cell = 5 - 6V).
    Plus on plus, minus on minus (otherwise you´ll shorten it!!!).

    Only a few seconds (not more then ten seconds).
    At least one contact should be detachable fast for emergency purposes (I usually press a metal rod against the batterie´s contact instead of attach it fix).
    Keep in contact to the batterie´s body with the back of a finger. If it gets hot, it is too much, disconnect at once!
    Don´t be worried, there´s plenty of time between the point of noticing the heat and the dangerous treshold of exploding the cell (provided you really connected not more but 6V. Those dramativ clips where cells are exploding were made by using the excessive voltage of 12V or more).
    If you have one, measure the voltage with a multimeter. You should reach at least 2.5V.
    If not, connect the contacts again for a few second (and stop when the cell gets hot). You can repeat this procedure several times. Just watch for the temperature (give the cell time to chill).
    If the voltage does not increase after several times, though you charged until the cell got hot, then the cell is definatly dead. Happened a few times to me, but in this cases, the cell´s voltage was 0.00 or 0.10V.

    You can also use a 9V cell (easy to get, easy to connect), just don´t forget to monitor the heat.

    Now, the current voltage of the cell is high enough to get charged commonly (some chargers accept 2.2V as a starting voltage). You should charge it immediatly with a common Li-Ion-charger, because the batterie´s voltage drops pretty fast again.
    Don´t try to drain energy out of the battery (i.e. don´t use it yet) until you´ve completely charged the battery in a common charger. If you have a charger with a reliable standby-circuit (i.e. a circuit, that keeps the cell permanently on 4.20V), keep it in the charging cradle for 14 more hours.

    I had tried this over years on some dozens cells and it worked on almost all of them pretty well, none exploded.
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  • Ghlargh Wednesday, June 03, 2009 7:37 AM Reply
    The high current technique is for NiMh and NiCd batteries.

    I repeat, you should recharge a dead LiIon or LiPo with LOW current, a few mA. NOT several amps.

    The low current method is the one recommended by a person who has a doctorate in Li* battery behavior, who's work i have read. It is also recommended by some manufacturers. One of the things on manufacturers lists of things never to do is to charge a cell at high current if it's very heavily discharged.
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  • Kleinalrik Wednesday, June 03, 2009 2:03 PM Reply
    It´s not the smoothest method. But it won´t do any much more harm to the cell than the overdischarging already committed.
    I repeat, I tried it over several years on dozens to hundreds cells and it worked pretty well in most occasions. And I´m talking about Li-Ion-cells (though it was originally meant for Ni-Cells).
    And it works quick (and dirty).
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  • Kleinalrik Wednesday, June 03, 2009 2:04 PM Reply
    The crucial thing is to do it only for a few seconds.
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  • spankyhank Tuesday, July 07, 2009 9:12 AM Reply
    Would connecting a 3.7v Li-ion (from a bluetooth headset) in series to a 1 or 2 AA batteries for a few hours do the job?
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  • Ghlargh Tuesday, July 07, 2009 10:52 AM Reply
    If you hook it up in series, you will recharge it backwards, totally destroying it, what you need to do is hook up a source parallel to the LiIon, and a low current source at that.

    This would work:

    Take your dead LiIon
    Hook 2 AA cells in series
    Hook the free minus pad of the 2AA to the LiIon's minus pad
    Connect a resistor of about 1k ohms between the free plus pad of the 2AA to the plus pad of the LiIon.

    This should carefully and slowly charge the LiIon up to 2.5-3V where a normal charger can take over.
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