NIMH charge longevity?

Discussion in 'Digital Photography' started by M. Souris, Sep 10, 2003.

  1. You shouldn't expect longer operating time from NiMH cells in low to
    medium drain applications. Alkaline cells have something like 2800 mAh
    capacity when used with a low-current load like a clock, and still
    something like 1800 mAh for a medium-current load like a GPS receiver.
    With these devices, one full NiMH charge is only about the same amount
    of energy as alkalines (GPS) or less than a set of alkalines (clock).

    The reason you get longer life in cameras is that alkalines are hopeless
    for camera use. They can't supply the current needed, and the camera
    stops working while the alkaline batteries still have most of their
    energy - they just can't deliver it.
    That's the worst possible type of charger. To fully charge a set of
    batteries without overcharging them, you have to discharge the
    batteries fully before recharging (which isn't good for them), then
    recharge for the full timed cycle (once, not twice). If the batteries
    aren't discharged before you start, or if you do the charge cycle
    twice, you'll overcharge the batteries (which will damage them).
    Finally, the timed period is correct for just one capacity of battery.
    If the charger is designed for 1200 mAh cells, it won't fully charge
    1600 mAh cells in one cycle, but it will overcharge them in two charge
    cycles. Use that charger as a doorstop, or throw it away.

    You should either get a slow (14 hour) charger, or a fast (3 hours or
    less) charger. The fast charger detects when the batteries are full and
    shuts off, no matter what state of charge they were in when you started
    charging. The slow charger has no intelligence at all, and so if you
    charge for the full 14 hours you will end up overcharging the batteries
    to some extent, but the charge rate is so low it doesn't cause damage.
    Both of these are better for your batteries than the timed charger.

    Dave Martindale, Sep 11, 2003
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  2. M. Souris

    Ron Hunter Guest

    It might be, if they get hot during charging, or it may just not
    completely charge them. More likely the former. You might get one of
    the smart chargers with some new 1800mAh or better batteries and that
    should do a better job for you.
    Ron Hunter, Sep 11, 2003
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  3. M. Souris

    y_p_w Guest

    Those batteries must be really old - I'm guessing made in the US or
    Mexico. Energizer has changed their AA source to a Japanese supplier -
    the same that supplies Sony, Sanyo, Maxell, and other brands. The
    current Energizer AA offering has a rated capacity of 2100 mAh,
    although there are still 1700 and 1850 mAh AA's floating around.

    There is also a small amount of current leakage in almost any
    electronic device.
    I think you probably also need to note that the amount of self-discharge
    is more like an exponential decay. It's not 1-2% of the max charge
    lost per day, but 1-2% of that day's charge lost.
    y_p_w, Sep 11, 2003
  4. Maybe they are old by manufacturing standards, but the local Fry's stores
    still have plenty in stock, ready to sell.

    I'm aware of the Maha smart-charger now... maybe I'll look into that, as
    well as higher capacity NiMH batteries.

    Daniel W. Rouse Jr., Sep 13, 2003
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