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AA Batteries

Discussion in 'Beginner Electronics' started by Sir Psycho, May 2, 2006.

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  1. Sir Psycho

    Sir Psycho Guest


    So many times i read in product manuals "dont mix old and new
    batteries", can someone tell me why?

    I have a wireless mouse and keyboard here and strapped for cash. Got
    some nice energizer batteries and i want to put one in the mouse and
    one in the keyboard. Each take two batteries each, any harm in mixing
    them up?
  2. CLV3

    CLV3 Guest

    The BIGGEST issue I see is the old one will wear out first, causing more
    battery changes aand in the long run being more expensive than if you put
    just new batteries in to begin with. There may be safety issues, I guess. I
    am just looking at efficiency issues.
  3. default

    default Guest

    Sounds like you could put two older batteries in one or the other
    mouse/keyboard . . . .

    I know of no real reason for not mixing batteries except it is false
    economy to take a new battery and put it with a near dead one - weak
    ones have higher internal resistance and power from the new one will
    be wasted warming up the older one. In a large battery pack, in a
    high current application, that warming could be significant - but two
    batteries, in a mouse or keyboard? No.

    The old one may be prone to leaking and ruining the device . . .

    The old/new mix will make it look as if the device eats batteries even
    though with fresh batteries it will last awhile. Customer doesn't
    always remember they were mixing batteries.

    They may be covering their corporate asses and playing it safe.

    I have an mp3 player that eats its single AAA battery in about four
    hours - I put them (any brand) in the recharger (by Rayovac for their
    NIMH and alkaline rechargables) and they are good to go for another
    four hours - I can do that about 6-10 times then they start failing in
    a couple of hours and are prone to leaking. I use it every day,
    recharge every other day, so I have a good feel for how it is working.

    Same thing works with alkalines for clocks and remote controls etc..
    Get a little more life out of them . . . Just watch for leakage
  4. Slavek

    Slavek Guest

    The main reason is he the combined internal impdance of two batteries.
    Connecting 2 batteries in series make the total impeadance as a sum of
    each so if the load consumes certain current the voltage will drop to
    the unsustainable level by power supply of the unit.
    The new alkaline battery has ~0.2ohms(good ones). The old one has
    There could be certain conditions of batteries internal impedance,
    their voltages and load impedance that creates reverse voltage on older
    battery resulting in quicker damaging that one. It is specially
    possible with pulsed load. So as for your loads (pulsed one) it can be
    more critical than for torch.
  5. Guest

    Yes...the new one can (eventually) attempt to "charge" the old one and
    cause it to leak...and prematurely discharge the new one. Put both new
    cells in the same device and both old ones in the other device. If you
    are so strapped for cash, find you wired mouse and plug in into the
    appropriate port.
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