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NiMH battery ratings?

Discussion in 'Electronic Components' started by Roy Smith, Aug 15, 2004.

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  1. Roy Smith

    Roy Smith Guest

    I've got so many gizmos that take AA batteries, I'm thinking of
    investing in a bunch of rechargeables. In the past I've had horrible
    luck with NiCD, so I'm thinking NiMH.

    I'm looking at the specs for a bunch of them
    (http://www.onlybatteries.com/items.asp?db=62) and see AA's rated for
    anything from 1400 mAH to 2300 mAH. How is this possible? Same
    chemistry, same size. I can see some small variation in capacity, but a
    factor of 1.6? Do brands really differ that much in capacity, or are
    the ratings just a crock?
     
  2. Just as AA cells had a low and high rating, there are also the same for Nickel
    metal hydride batteries.

    Also note that 'some' capacities may be quoted at different discharge rates
    which will throw up different capacities, and lastly also note that consumer and
    industrial cells can be different again.

    In the days when Nicads were popular, 'C' cells came in industrial 2AH or 2.2AH,
    but consumer cells were only 1.2AH, and often consisted of an RR cell inside a C
    cell casing. Same with the D cell, industrial was 4AH or 4.5AH, consumer was
    2AH, C cell in a D casing.

    Peter
     
  3. Tim Wescott

    Tim Wescott Guest

    Battery construction can significantly affect the capacity. In general
    making the battery cheaper will decrease capacity, as will making it
    capable of high discharge current.
     
  4. Dave VanHorn

    Dave VanHorn Guest

    Good engineering, or good marketing BS.
    Nope, but stick with name brand cells from a reputable disti.
    Sanyo "C" type NIMH cells are quite good, but about double the price of the
    cheap chinese knockoffs. These cells have nearly the overcharge tolerance of
    Nicads, at the expense of a little capacity. They are slightly less
    amp/hours than the highest capacity sanyo cells. The knockoffs have good
    capacity, but may lack proper vents, or excess plate capacity, or the
    expensive catalyst for hydrogen/oxygen recombination. When that happens, a
    charged cell is also an armed thermal grenade. I've seen these cells spew
    boiling electrolyte strong enough to strip two layers off a 4 layer PCB in
    seconds. I've seen them "go nuclear" up to 24 hours after a perfectly normal
    charge. Most of them work just fine, but a few percent have problems.
     
  5. Don't bet on anything when it comes to some of these guys.. I know a
    US specialty consumer products company that had to throw away tens of
    thousands of custom battery packs because they were something like
    20%-25% lower mAh capacity than rated.

    Best regards,
    Spehro Pefhany
     
  6. Guest

    ------- Original text edited to fit 80 columns -------

    Right Peter - here's more battery "truth in advertising" from Tricia's
    website: http://www.tactical-link.com/wierd_stuff.htm

    D.
     
  7. That certainly shows the truth!

    There is/was a similar thing with the 6V lantern batteries, the Gates/GE
    rechargeable were 2.5AH but the dry battery was much larger in capacity.

    The 21.5AH battery had a resistor inside to restrict charge/discharge current.

    Peter

    --
    Peter & Rita Forbes
    Email Address:

    Web Pages for Engine Preservation:
    http://www.oldengine.org/members/diesel
     
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