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Thread: Is It Necessary To Discharge NiMH AA & AAA Batteries Before Recharging Them

  1. #1
    Enlightened
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    Popcorn Is It Necessary To Discharge NiMH AA & AAA Batteries Before Recharging Them

    I'm an Ornithologist and I do a great deal of night work in the study of Owls and Bats. I also do some work in other wildlife research that includes night work. And I run a number of Nesting Box Research Projects and rely heavily on my Headlamps and Flashlights. My research team and myself have decided to switch to 2700 nAh NiMH AA's in our PT Apex Headlamps and 1000 mAh NiMH AAA's in our PT EOS Headlamps.

    With older rechargeable batteries it was always necessary discharge the batteries before recharging them. I was told that the new NiMH Batteries don't have a memory effect and don't require discharging before charging. My 8 bay LED Battery Charger from Amondotech.com has a refresh feature, to discharge the batteries before recharging them and that what I've be doing. However, I've been told be some this in not needed, yet other say it's better to discharge before charging.

    I don't think what I'm doing will harm the batteries, but is what I'm doing just a waste of time?
    Best regards,
    GCB Stokes
    Avian Wildlife & Nesting Box Research And Studies
    And Avid Outdoorsman

  2. #2
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    Default Re: Is It Necessary To Discharge NiMH AA & AAA Batteries Before Recharging Them

    Hello GCBStokes,

    Just charge them up and use them.

    A full discharge is good to do every 30 - 50 cycles, but is not necessary every time.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

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    Flashaholic* AFAustin's Avatar
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    Default Re: Is It Necessary To Discharge NiMH AA & AAA Batteries Before Recharging Them

    Quote Originally Posted by SilverFox
    Hello GCBStokes,

    Just charge them up and use them.

    A full discharge is good to do every 30 - 50 cycles, but is not necessary every time.

    Tom
    Tom, could I please ask a couple of follow-ups?

    1) If you don't have a charger with a discharge function, and so are just doing your periodic discharge by means of running the NiMHs in a light, at approx. what voltage should you stop the discharge?

    2) If you use certain NiMH cells infrequently, should you go ahead and do a full discharge every, say 3 mos., or just not worry about it till you get to at least 30 cycles?

    Thanks very much,

    Andrew

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    Default Re: Is It Necessary To Discharge NiMH AA & AAA Batteries Before Recharging Them

    Hello Andrew,

    A cell is considered fully discharged at 1.0 volts, under a light load, or 0.9 volts, under a heaver load. Resting, open circuit, voltage should come back to around 1.15 - 1.20 volts after the load has been removed.

    When you store NiMh cells, discharge them to 1.0 volts under a moderate load before storage. If you are interested in peak performance from your cells, run through a charge/discharge cycle every 30 days. If your needs are "less demanding," you can put off the charge/discharge cycle for 3 or 6 months, or until the cell voltage has dropped below 1.2 volts.

    If you anticipate long storage (1 year) and not being able to access your cells, you can discharge them, then do roughly a 25% charge on them. This is roughly how they come from the factory.

    Tom

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  5. #5
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    Popcorn Re: Is It Necessary To Discharge NiMH AA & AAA Batteries Before Recharging Them

    Tom,

    Hello GCBStokes,

    Just charge them up and use them.

    A full discharge is good to do every 30 - 50 cycles, but is not necessary every time.

    Tom
    Thanks, that will save time charging when on the road or working in the field. Wayne over at Amondotech.com also had told me it was not necessary as well. He seems pretty strait up and accurate with answers, but it doesn't hurt to have a second opinion. A few of the researchers I work with were a little worried about the memory effect problem that was seen with older batteries.

    I've learn a lot about the NiMH Batteries recently. I also just found out that the new NiMH Batteries will work well at temperatures down to Zero (0) Degree F.! So, I'm replacing all of my older NiMH Batteries and replacing them with new ones. The more I learn about the new NiMH rechargeable AA & AAA Batteries, the more I believe they will be pretty much the only batteries I'll use. I'll keep some Lithium AA & AAA for emergencies, or extended backpacking or camping trips where there is no way of recharging NiMH Batteries. But that won't be too often, most of the camping I do these days is camp ground camping in State and National Parks with the wife and kids, where we always have access to our vehicles to charge batteries with the charger plugged into the cigarette lighter.

    Take care and thank you again for your expert advice.

    George
    Last edited by GCBStokes; 03-14-2007 at 02:51 PM. Reason: corrections
    Best regards,
    GCB Stokes
    Avian Wildlife & Nesting Box Research And Studies
    And Avid Outdoorsman

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    Flashaholic* AFAustin's Avatar
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    Default Re: Is It Necessary To Discharge NiMH AA & AAA Batteries Before Recharging Them

    And thanks from me as well, Tom, for the additional info.

    Andrew

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