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AA Battery Pole Reversal

Discussion in 'Electronic Repair' started by Douglas C. Neidermeyer, Dec 19, 2011.

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  1. Subject says it all. I pulled and tested the two name brand AA cells in
    my dead MagLite and found one cell reading weak and the other with the
    poles reversed-- negative at the top nipple, positive at the round base.
    Rechecked with another meter-- same result.

    What's that all about?
  2. It's called "cell reversal". It's most-common with rechargeable devices
    using nicad or NiMH cells, but I also saw it in an HP calculator that used
    alkaline N cells.

    Here's what happens... One of the cells has significantly lower capacity
    than the others. When it hits zero volts, the other cells are pumping
    current through it /in reverse/. This causes the cell to charge up
    backwards, with reversed polarity.
  3. Thanks William and Dave for the explanation.

    I had saved the two alkaline batteries that I pulled about 10 days ago
    and just retested them. One was still weak, the other (presumably the
    one with the reversed polarity) is stone cold dead.
  4. Phil Allison

    Phil Allison Guest

    "Dave Platt"

    ** There are warnings printed on most Alkaline cells against attempting to
    recharge, improper insertion and disposal in a fire.

    The funny thing is that with a device using 4 or more such cells, the simple
    mistake of inserting one cell backwards will result in breaking all the
    above rules.

    1. The reverse inserted cell will be charged by the others.

    2. Pressure will build up inside it and it WILL explode and make one hell
    of a mess.

    Very good reason not to let kiddies play with alkaline or other high energy

    .... Phil
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