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Thread: Tool battery cells at 6mV

  1. #1

    Default Tool battery cells at 6mV

    I took apart a few "Bad" Milwaukee 18v redlithium batteries to see if I could repair them like I have in the past or at least scavenge the cells. Problem is all 15 cells from 3 different packs read between 6mV-300mV. It's not a multimeter issue, it works fine and I checked with another meter as well.

    I find it very odd that all of the cells are like this. I've taken apart many other tool brand battery packs and never seen this before. Does Milwaukee use protected cells by chance?

  2. #2
    Flashaholic*
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    Default Re: Tool battery cells at 6mV

    It's pretty easy to see if the individual cells are protected, but chances are they're not. You wouldn't be reading 0.3v from a tripped protected cell, anyway.

    So, if you're sure your DMM is accurate (and is using good batteries itself), then, yeah, those cells are probably junk. Probably ran down in the tool, then left for a long time to trickle-discharge in the BMS.

  3. #3
    Flashaholic
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    Default Re: Tool battery cells at 6mV

    I've recovered non-protected 18650's from laptop battery packs (with great caution I add). Anything reading
    such low voltage goes to recycle. A proper charger might be able to recharge them starting with initial trickle charge
    until they reach 2.5v or so (if they can), but probably not in good shape and not worth it.

    Dave

  4. #4
    Flashaholic*
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    Default Re: Tool battery cells at 6mV

    Yeah, I think my Xtar chargers will recover 0v cells, doing a trickle charge until they get up to around 3v (somewhere around that level), then charging normally. But, I wouldn't trust a cell that was depleted that far, especially for what may have been a long time. Even if there's a 99% chance it will be fine, that 1% isn't worth the risk IMO. Maybe for an outdoor solar light, but nothing I would put in my pocket.

  5. #5

    Default Re: Tool battery cells at 6mV

    Quote Originally Posted by WalkIntoTheLight View Post
    Yeah, I think my Xtar chargers will recover 0v cells, doing a trickle charge until they get up to around 3v (somewhere around that level), then charging normally. But, I wouldn't trust a cell that was depleted that far, especially for what may have been a long time. Even if there's a 99% chance it will be fine, that 1% isn't worth the risk IMO. Maybe for an outdoor solar light, but nothing I would put in my pocket.
    What Xtar charger can recover them?

  6. #6
    Flashaholic*
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    Default Re: Tool battery cells at 6mV

    Quote Originally Posted by novarider View Post
    What Xtar charger can recover them?
    IIRC, I think almost all of them. Even my tiny MC1 does it. I usually use a X4, and I can tell it does the recovery very slowly at first, because that's how it starts the first few minutes with a NiMH cell. It trickles it for a few minutes, to see if the voltage comes up. After a few minutes, if the voltage is still low, it assumes it is NiMH and ramps up the charging current. So, that must be how it recovers low-voltage lithium-ion.

    I think Xtar refers to their charging algorithm as TC/CC/CV. The TC I presume stands for "trickle charge", which is used when the cell has very low voltage.

    I'll over-drain an old cell I no longer use, and give it a try in the next couple of days. Just to be sure.

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