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Products specifying alkaline batteries

Discussion in 'Electronic Repair' started by BE, Oct 11, 2006.

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  1. BE

    BE Guest

    I have an electronic scale that uses a 9v battery and it says "use alkaline
    batteries only". I prefer to use rechargeable NiMH batteries. How can the
    product tell the difference (or can it) and what would be the problem, if
    any, of using non-alkaline batteries in such a product.

    Thanks,
    noozer
     
  2. Meat Plow

    Meat Plow Guest

    As they discharge, the voltage drops off more linear in an alkaline. The
    rechargable stays more constant then drops off rapidly. Hence the scale
    will operate longer on an alkaline.
     
  3. Puckdropper

    Puckdropper Guest

    Rechargable batteries tend to have a lower voltage than non-rechargable,
    so the voltage difference might cause trouble. My guess is the "Use
    alkaline batteries only" is there because the manufacturer knows the
    device likes to eat batteries for breakfast, lunch, and dinner.

    Puckdropper
     
  4. Maybe more important, rechargeables don't start with the same voltage
    level as fresh alkalines, and if the unit counts on the voltage being
    above a certain point, the useable "life" of the rechargeable will
    not be so long (though of course, they can be recharged).

    I used to have something, it might have been my Radio Shack Model
    100 laptop, that I used rechargeables in, and they sure didn't last
    as long as alkalines. On the other hand, the rechargeables could
    be recharged so I got more long term life out of them than the alkalines.

    Michael
     
  5. The bottom line is it almost certainly won't hurt the equipment so may be
    worth trying. For something like an electronic scale, rechargeables
    may indeed be fine.

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  6. Ken Weitzel

    Ken Weitzel Guest

    Hi...

    The voltage of a brand new alkaline is 1.5 volts. The
    voltage of a freshly charged nimh or nicd is 1.2 volts.

    The likelihood is that your scale will see the 1.2 volts,
    and decide that the battery is due for replacement - at worst
    refuse to operate; at best tell you to change the battery.

    Take care.

    Ken
     
  7. CJK

    CJK Guest

    Or pehaps the current drain is so low that alkalines will last for years,
    and rechargables will self discharge in days to weeks. For low drain
    devices like clocks, calculators, and scales with LCD displays, or other
    infrequently used devices, rechargables do not really make sense. Alkalines
    have a shelf life of several years.

    CK
     
  8. However, the terminal usable voltage of an alkaline will be very similar
    to that of a Ni-Cad, etc.
     
  9. Eeyore

    Eeyore Guest

    I discovered recently that Duracell quote battery lifetime to 50% of initial
    voltage ! Any rechargeable will be far better.

    Graham
     
  10. Eeyore

    Eeyore Guest

    According to Duracell, an alkaline battery isn't dead until it reaches 0.75V !

    Incidentally, you can get '9V' alkalines with 7 or 8 cells ( 8.4 or 9.6 V ).

    Graham
     
  11. James Sweet

    James Sweet Guest

    You mean NiCd? Most "9V" rechareables are 7.2V. 9V alkaline batteries
    consist of 6 1.5V cells which add up to an even 9V.
     
  12. Jim Yanik

    Jim Yanik Guest

    Does anyone MAKE a "9V" NiMH battery?
     
  13. Jim Yanik

    Jim Yanik Guest


    For an electronic scale,I'd use a wallwart.
     
  14. Jim Yanik

    Jim Yanik Guest

    Very good point!
     
  15. Jim Yanik

    Jim Yanik Guest

    actually,it's more like 1.4v
     
  16. Eeyore

    Eeyore Guest

    NiMH. I don't know what made me type alkaline !

    I have one right here that I recharged a month or two ago and its current terminal
    voltage is 8.99V.

    Graham
     
  17. Eeyore

    Eeyore Guest

    I have one in front of me ( a cheapie ) that I recharged a month or two
    back.

    It currently measures 8.99V.

    Graham
     
  18. Eeyore

    Eeyore Guest

    1.3 but not for long.

    Graham
     
  19. BE

    BE Guest

    I just bought several Energizer Rechargeable "9v" batteries (NiMH) and,
    thanks to a previous post, I looked at the fine print and, yes, it is
    actually 7.2volts! It says: "Size 9v" - so they can claim it is a 9v
    battery due to the loose use of the term "9v" to indicate a "size" rather
    than a power potential.

    Why would the makers of these rechargeables make them not truly match the
    voltage they are supposed to be?

    noozer
     
  20. Because it's a chemical matter.

    A cell puts out about 1.5v. If you need more voltage, you combine them.
    So when the need for 9v batteries came along, they had to combine six
    cells in the package. Or maybe they decided on package size, and then
    picked a voltage that would fit the package. Open up a 9v battery,
    and you'll see six invidual cells. In some, it's 6 sort of lumps, but
    in others it's sort of like skinny AAA cells inside. If they needed
    more voltage, they'd have to add more cells, and the package would be
    bigger for the same amount of current.

    Nicads put out about 1.2v. That too is a chemical issue. The only
    way they can get a higher voltage is by combining cells in the same
    package, but that cuts current capacity (since the cells would
    be smaller), and results in not the needed 1.5v but 2.4 volts.

    So when they combine 6 nicad cells in a "9v battery" package,
    6 * 1.2 =7.2volts. Again, the only way to fix that is by putting
    mroe cells inside that package, and while that's more feasible than
    with a straight AA cell, it forces each to be a physically smaller
    cell and that likely impacts on the current the whole thing
    can supply.

    In some cases, equipment has been designed with all this in mind.
    The battery compartment will be big enough to accomodate more
    batteries than the needed voltage would require in alkaline batteries.
    So that old CB walkie talkie would have a place for 10 AA batteries,
    so if they are nicads it gets 12v. It would then come with a pair
    of dummy AAs, that merely fill space and provide contact end to end,
    so when using alkaline AAs you would simply put in 10 AAs and the
    dummies, and still get 12volts.

    Michael
     
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