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NiMh batteries problem

Discussion in 'Off-Topic Members Lounge' started by hobbyist, Aug 4, 2013.

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  1. hobbyist

    hobbyist

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    Aug 4, 2013
    Just bought set of four "Songpus" AA rechargeable batteries from Ebay claiming to have 4700 mAh charge rating. Thought it looked too good to be true; now wondering if it was. Put them on crude discharge test (1 ohm resistor in series) with each, producing just over I amp starting current, and obtained discharge to 0.2 volts in only 25 to 30 minutes.
    Substituting 2ohms resistor produced discharge to 0.2 volts n 63 to 68 minutes. Batteries were initially charged with Uniross fast charger at 1 amp.

    Anyone with similar experience, before I formally complain to Ebay?

    hobbyist
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    4700mAH for NiMh sounds like snake oil to me. My strongest cells claim 2700mAh and I'm quite sure they do not stand up to their promise.

    The capacitiy of a cell depends on the discharge current. The higher the curent the hotter the cell becomes, meaning that more power is cónverted to thermal energy and is therefore not available in electrical form. Here is a webpage with some information on testing battery discharge behaviour. This page clearly shows this effect.

    Can you post a link to the ebay sales page for the batteries?
     
  3. hobbyist

    hobbyist

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    Aug 4, 2013
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Did it look too good to be true?
     
  5. hobbyist

    hobbyist

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    Aug 4, 2013
    I did wonder at the time. Trouble was I hadn't lately checked the status of NiMh for some time although I knew it was improving by leaps and bounds. So here these things were, apparently very reasonably priced for what they professed to be, so Billy Muggins thought he'd give 'em a try.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I would be complaining that they're not as described. Whilst their capacity is probably higher at a lower current, the time you report indicates the capacity is nowhere near what is claimed.

    you're seeing well under 1000mAh, and probably closer to half of that
     
  7. hobbyist

    hobbyist

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    Aug 4, 2013
    Ok Steve, I'm taking this up with Ebay. I'll post the outcome here.
     
  8. hobbyist

    hobbyist

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    Aug 4, 2013
    Hope this isn't double posting - last attempt disappeared after hitting Submit button. Hadn't logged in or something.

    Decided to drop this case; don't see any chance of a positive resolution. As a matter of interest, though, I'm wondering if the weight of an NiMH cell has any bearing on the charge capacity of that chemistry, ie., the heavier it is the greater the capacity? I ask this because I noticed that these 'wonder' batteries felt lighter than a Duracell NiMH that I have (latter around 2400mAh). On weighing them, Duracell was about 30 gms, Songpus about 15 gms. Half the weight, nearly twice the energy?..Wow.
     
  9. GreenGiant

    GreenGiant

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    Feb 9, 2012
    the weight is not a huge factor, its all about specific composition of the batteries, I worked with LiPO batteries that would vary in weight drastically but sometimes the weightier ones would have lower capacities.

    I really think that you got taken for a ride on this one, the best LiPO batteries of that size are a little smaller in capacity (around 2.3Ah) and thats around 3.6V and even the "oxide" ones which go a little higher in voltage aren't even able to come close to the 4.7 claim (oxides are about 3Ah at 4.2V)
     
  10. shrtrnd

    shrtrnd

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    Jan 15, 2010
    I agree that the aH rating sounds untrue, and that you were probably taken.
    I did get a batch of Duracell NiMH batteries once that I initially thought were garbage.
    But I cycled them half a dozen times, and they finally started holding their charge,
    you might want to try that.
    Only other things I can think of:
    1) Are you sure they're NiMH, not NiCad or Lithium?
    2) Are you charging them with the correct charging circuit for battery type?
    Kind of surprised Ebay isn't backing this up with their warranty.
     
  11. hobbyist

    hobbyist

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    Aug 4, 2013
    1)Can't be sure of anything here. NiMH is stated on the cells.
    2)only possess Uniross quick charger which charges at 1A. If the cells are kosher, that's just a bit over their C/5 rate. After discharge they took about 10 minutes to show full charge. Ebay are prepared to back me up, but I'm not pushing it; it was becoming unpleasant; not worth it for sake of 6 or 7 quid.
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I've heard of bogus rechargeable D cells that were made by putting an AA cell inside a D-sized case. Perhaps that's why they're so light.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Please be sure to leave accurate feedback. Even if you're not prepared to fight it, at least do your best to alert others.
     
  14. hobbyist

    hobbyist

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    Aug 4, 2013
    Trouble is not 100% sure items are dud or fake; not time to try several accelerated recycles yet. Secondly, guy's customer feedback for this item shows at least 6 happy customers and no negative feedback. I need time and testgear to do thoro investigation.
    I shall try to do this before the Ebay complaint time allocation expires.
    Only possible real indicator at present that these are fakes might be their weight (half that of typical cell), but Green Giant has said weight is not a factor.
     
  15. hobbyist

    hobbyist

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    Aug 4, 2013
    I suppose that's possible explanation for the weight, and it's been said many C batteries legitimately on the market are just dressed up AA batteries. But if these batteries are using that dodge they'd have to be AAAs or smaller. That makes it even less likely they could pack a 4.7Ah charge, so you could just be right.
     
  16. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Oh sorry. I had the idea that your batteries were D size. Probably because of the high claimed capacity figure. But they're AAs.

    I guess they could be AAA internally, but there's little reason to do that, because the cost difference between AAAs and AAs is not much compared to the cost difference to C or D cells. You could sacrifice one and find out though.
     
  17. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Off subject, but like KrisBlueNZ said, in the past Radio Shack DID put 'AA' batteries
    inside of 'D' cell packages. I saved a couple of them so I could prove to disbelievers
    I've talked to in the past about this.
    I'm wondering if maybe this 'quick charger' might be the problem here (factory defect?),
    10 minutes for a recharge seems to me to be pushing the envelope. If that 'trickle
    charge' is a little high, it might be the problem (and would kill the batteries quick).
     
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