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Thread: NiMH AA's hot after testing (+ terminal)?

  1. #1

    Default NiMH AA's hot after testing (+ terminal)?

    I had some older NiMH AA's that I ran through three conditioning cycles (all "soft" recharge) on my Maha MH-C808M. After the third cycle, I left them sitting for at least an hour before checking them with my ZTS MBT-1 tester. They weren't hot or even warm before testing, even when fresh out of the charger. All of them showed 100% on the MBT-1.

    I had four of them in my left hand, getting ready to put them into the battery holder of the device in which I use them, and suddenly felt a burning sensation on my ring finger.
    I let go of them in a hurry. I don't see any blistering or even a red mark, but this isn't the first time I've run across this.
    Before I had the pulse load testers, I'd check batteries with a cheapie digital voltmeter. At least once while holding the DVM probes onto the respective terminals on a battery, I've noticed some uncomfortable heat from the positive probe. Again, not enough to cause injury, but enough to make me let go of it quickly and say "ouch," or words to that effect.

    Is this something wrong with those batteries, or do I just need to change my battery testing techniques? I don't think the positive terminal on the battery or the DVM probes made contact with my wedding band, but I s'pose that could have happened. Unless both terminals had somehow been connected, though, I can't see how any kind of short circuit occurred. My hands weren't wet, and I don't think I'm that good a conductor.

  2. #2
    Silver Moderator
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    Jan 2003
    Bellingham WA

    Default Re: NiMH AA's hot after testing (+ terminal)?

    Hello Train Watchman,

    Very interesting...

    It almost sounds like there may be an internal short in the cell. Usually heat builds up during the charge, then the cell cools off when the charge is complete. If you didn't physically short the cell out any heat indicates an internal issue.

    Unfortunately, there isn't an easy way to check this out. Often, internal shorts will burn themselves out and the next test cycle will appear as normal.

    When I run into cells that "misbehave," I recycle them and move on. You will have to make the call on this.

    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  3. #3

    Default Re: NiMH AA's hot after testing (+ terminal)?

    Thanks, Tom. I haven't run across it for awhile, so maybe it was just a transient thing. Maybe it blew out any "whiskers" inside those cells, and corrected itself. (Or I might have just imagined it. )

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