While discharging, battery voltage increases?

Discussion in 'Digital Photography' started by John Doe, Dec 12, 2008.

  1. John Doe

    John Doe Guest

    I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    milliamps. After the first minute or so it shows 1.05 V. Between then
    and three hours later, the voltage steadily rises to 1.08 V. Is there
    something wrong with the battery analyzer, or can battery voltage
    increase very slightly as the battery discharges?

    Or maybe I'm reading the analyzer voltage that produces the 500
    milliamps through the battery? And that's the voltage required to
    produce the 500 milliamps? As expected, several other batteries show
    the voltage levels decreasing as they discharge, but this one is
    consistently unusual.

    I'm using the Maha PowerEx MH-C9000 battery charger/analyzer.

    Thanks.
    John Doe, Dec 12, 2008
    #1
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  2. John Doe

    Phil Allison Guest

    "John Dope"

    > I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    > milliamps. After the first minute or so it shows 1.05 V.



    ** So it is completely flat in one minute ??????????

    Wot asinine drivel is this brain dead cretin on about now ??





    ....... Phil
    Phil Allison, Dec 12, 2008
    #2
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  3. John Doe

    Phil Allison Guest

    "BobWanker"
    > "John Dope"
    >> I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    >> milliamps. After the first minute or so it shows 1.05 V. Between then
    >> and three hours later, the voltage steadily rises to 1.08 V. Is there
    >> something wrong with the battery analyzer, or can battery voltage
    >> increase very slightly as the battery discharges?
    >>
    >> Or maybe I'm reading the analyzer voltage that produces the 500
    >> milliamps through the battery? And that's the voltage required to
    >> produce the 500 milliamps? As expected, several other batteries show
    >> the voltage levels decreasing as they discharge, but this one is
    >> consistently unusual.
    >>
    >> I'm using the Maha PowerEx MH-C9000 battery charger/analyzer.
    >>


    >
    > It's probably not applying a constant load to the battery.



    ** Correct - but can you also explain the unusual behaviour of just one
    particular cell?

    And the wrong voltage reading.

    1.05 volts = a flat cell.



    ....... Phil
    Phil Allison, Dec 12, 2008
    #3
  4. John Doe

    Jasen Betts Guest

    On 2008-12-12, John Doe <> wrote:
    >
    > I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    > milliamps. After the first minute or so it shows 1.05 V. Between then
    > and three hours later, the voltage steadily rises to 1.08 V. Is there
    > something wrong with the battery analyzer, or can battery voltage
    > increase very slightly as the battery discharges?


    change of temperature could do that possibly?
    Jasen Betts, Dec 12, 2008
    #4
  5. John Doe

    ransley Guest

    On Dec 11, 8:27 pm, "Phil Allison" <> wrote:
    > "John Dope"
    >
    > > I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    > > milliamps. After the first minute or so it shows 1.05 V.

    >
    > ** So it is completely flat in one minute ??????????
    >
    > Wot asinine drivel is this brain dead cretin on about now ??
    >
    > ......  Phil


    Load probably varies,
    ransley, Dec 12, 2008
    #5
  6. John Doe

    Martin Brown Guest

    Phil Allison wrote:
    > "BobWanker"
    >> "John Dope"
    >>> I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    >>> milliamps. After the first minute or so it shows 1.05 V. Between then
    >>> and three hours later, the voltage steadily rises to 1.08 V. Is there
    >>> something wrong with the battery analyzer, or can battery voltage
    >>> increase very slightly as the battery discharges?
    >>>
    >>> Or maybe I'm reading the analyzer voltage that produces the 500
    >>> milliamps through the battery? And that's the voltage required to
    >>> produce the 500 milliamps? As expected, several other batteries show
    >>> the voltage levels decreasing as they discharge, but this one is
    >>> consistently unusual.
    >>>
    >>> I'm using the Maha PowerEx MH-C9000 battery charger/analyzer.
    >>>

    >
    >> It's probably not applying a constant load to the battery.

    >
    > ** Correct - but can you also explain the unusual behaviour of just one particular cell?
    >
    > And the wrong voltage reading.
    >
    > 1.05 volts = a flat cell.


    But there is something odd happens with matched sets of NiMH batteries
    in some digicam applications. I have several sets for a Pentax istD
    digicam. What I have noticed is that one cell always appears weaker
    than all the others by a significant margin and the camera fails early
    with "low battery" when NiMH cells are used ending up with 3 good ones
    and one flat. The first one to go flat kills it. The odd thing is that
    I suspect the flat is almost always in the same battery slot - as if
    there is some extra burden on that specific cell. Using flash heavily
    or excessive cold generally tips it over the edge more quickly.

    I have taken to putting dots on the failing cells but there is no
    obvious pattern - it isn't same cell failing every time due to higher
    self discharge or internal factors. I have noted the position where
    the cell most likely to fail resides and swap it out on failure. This
    usually works and has better odds than perm 4 from 8 with 2 duds.

    More curious still single use Duracells with higher terminal voltage
    which I use when the NiMH have all died always seem to discharge
    evenly. I would be interested if anyone can explain this.

    Regards,
    Martin Brown
    Martin Brown, Dec 12, 2008
    #6
  7. John Doe

    Don Stauffer Guest

    John Doe wrote:
    > I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    > milliamps. After the first minute or so it shows 1.05 V. Between then
    > and three hours later, the voltage steadily rises to 1.08 V. Is there
    > something wrong with the battery analyzer, or can battery voltage
    > increase very slightly as the battery discharges?
    >
    > Or maybe I'm reading the analyzer voltage that produces the 500
    > milliamps through the battery? And that's the voltage required to
    > produce the 500 milliamps? As expected, several other batteries show
    > the voltage levels decreasing as they discharge, but this one is
    > consistently unusual.
    >
    > I'm using the Maha PowerEx MH-C9000 battery charger/analyzer.
    >
    > Thanks.


    If the analyzer is applying only a light load, that is possible- the
    battery heats up a bit, and the light load voltage is temperature
    dependent. But 500 mA is not a light load, so that is surprising if it
    REALLY is discharging at that rate.
    Don Stauffer, Dec 12, 2008
    #7
  8. John Doe

    ASAAR Guest

    On Fri, 12 Dec 2008 06:09:53 -0800 (PST), Martin Brown wrote:

    > But there is something odd happens with matched sets of NiMH batteries
    > in some digicam applications. I have several sets for a Pentax istD
    > digicam. What I have noticed is that one cell always appears weaker
    > than all the others by a significant margin and the camera fails early
    > with "low battery" when NiMH cells are used ending up with 3 good ones
    > and one flat. The first one to go flat kills it. The odd thing is that
    > I suspect the flat is almost always in the same battery slot - as if
    > there is some extra burden on that specific cell. Using flash heavily
    > or excessive cold generally tips it over the edge more quickly.


    I've noticed that as well, but it's to be expected when the
    batteries are used too long between recharges. Cells in a matched
    set don't all have the same capacity. They're just placed in sets
    that have tighter tolerances, but one of them will *always* be have
    less capacity than the rest, and this 'weaker' cell will be the
    first to die.


    > More curious still single use Duracells with higher terminal voltage
    > which I use when the NiMH have all died always seem to discharge
    > evenly. I would be interested if anyone can explain this.


    Alkaline and NiMH batteries may have large differences in their
    measured voltage curves as they're used, but both really discharge
    fairly evenly. The big difference is that alkalines don't have
    voltages that decline precipitously when they're nearly exhausted.
    If you measure individual voltages of alkaline cells as they're
    used, there may be differences, but they're fairly close, and they
    remain usable at much lower voltages than rechargeables. If
    measured, you'll probably find voltages clustered around 1.1v, 0.9v,
    0.7v and 0.5v. Using the last as an example, with 4 AA cells you
    might measure 0.53v, 0.50v, 0.48v and 0.47v under load. Cameras are
    different in that they tend to require slightly more than 1.0 or 1.1
    volts per cell to keep operating. When cameras exhaust their AA
    alkaline cells, they're far from being really exhausted, will
    probably show more than 1.2 volts if measured without a load, and
    can continue to be used for hours, sometimes many dozens of hours in
    devices that don't require high loads, such as analog radios (at low
    or medium volume), LED lights, etc.

    NiMH cells also discharge uniformly, but at the point were they're
    nearly exhausted (somewhere between 1.1v and 1.0v) the first to
    become completely exhausted will show a very rapid drop in voltage
    as it plunges from 1.0v to 0.0volts. The remaining 3 NiMH cells
    will still be pumping out more than 3.0 volts and you'd really want
    the device they're powering to shut down at this point, because if
    it doesn't, the depleted cell will start to become reverse charged,
    damaging or killing it. This is true even though the 3 remaining
    cells may have less than 1% of their capacity remaining. Most
    digital cameras require more than 3.0volts to operate, so they won't
    tend to kill NiMH cells, but if you don't remove them for recharging
    until the camera shuts down, one of the cells is pretty much
    guaranteed to appear near dead in a battery tester. The harm in
    doing this repeatedly depends on the individual camera, ie, at how
    low the voltage of the complete battery set has to go before it
    shuts down. At the point that digital cameras shut down when
    alkalines are used, they'll have a good deal of unused capacity, and
    can probably provide a little more than 1.1 or 1.2 volts under light
    loads to other devices for a long time.

    It's possible that one or two cells may be loaded more heavily in
    certain slots, and if that's the case it might be to provide a lower
    voltage for clock or memory chips at very low currents. In this
    case the effect would be noticeable only if the devices are used
    very intermittently, where the batteries would last quite a while
    before needing to be replaced, depending on design anywhere from a
    couple of months to a year or more. This can be ruled out if you
    open the case and check the battery compartment to see if it has no
    more than two wires connecting the device to the battery pack.
    ASAAR, Dec 12, 2008
    #8
  9. John Doe

    Dave Cohen Guest

    John Doe wrote:
    > I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    > milliamps. After the first minute or so it shows 1.05 V. Between then
    > and three hours later, the voltage steadily rises to 1.08 V. Is there
    > something wrong with the battery analyzer, or can battery voltage
    > increase very slightly as the battery discharges?
    >
    > Or maybe I'm reading the analyzer voltage that produces the 500
    > milliamps through the battery? And that's the voltage required to
    > produce the 500 milliamps? As expected, several other batteries show
    > the voltage levels decreasing as they discharge, but this one is
    > consistently unusual.
    >
    > I'm using the Maha PowerEx MH-C9000 battery charger/analyzer.
    >
    > Thanks.


    I have an .mp3 player that uses a single AAA. I notice the charge
    indicator on the device starts of full, shows partial charge after usage
    and will return to show a full charge when next turned on. Never really
    gave the matter much thought.
    Dave Cohen
    Dave Cohen, Dec 12, 2008
    #9
  10. John Doe

    John Doe Guest

    patrick chilton <> wrote:

    <snip detailed explanation>

    > To confirm if its the charger/analyzer or the battery:
    >
    > Try putting the "bad" battery into a different slot in the
    > analyzer compared to a known good one in the same slot that the
    > "bad" battery was in. If the known good one acts as the "bad" one
    > then you know the analyzer is bad.


    > 0.03v is really not something to worry about.


    I was partly curious. After a charge/discharge/charge cycle, I
    switched the two batteries and started discharging them again at 500
    milliamps, paying closer attention. The bad battery in the other
    slot rose from about .96 V slowly and steadily upwards. Later, after
    it reaches 1.15 V or whatever and is significantly discharged, it
    probably starts going back downwards (as I recall from the last
    time). Still, it charged to a higher capacity than the other same
    type battery. I just threw it away.

    Batteries are not nearly consistent as I would have guessed.



    --
    thanks to the replies
    John Doe, Dec 13, 2008
    #10
  11. John Doe

    MuMu Guest

    On Dec 11, 8:12 pm, John Doe <> wrote:
    > I'm discharging a nickel metal hydride (NiMH) AA battery at 500
    > milliamps. After the first minute or so it shows 1.05 V. Between then
    > and three hours later, the voltage steadily rises to 1.08 V. Is there
    > something wrong with the battery analyzer, or can battery voltage
    > increase very slightly as the battery discharges?
    >
    > Or maybe I'm reading the analyzer voltage that produces the 500
    > milliamps through the battery? And that's the voltage required to
    > produce the 500 milliamps? As expected, several other batteries show
    > the voltage levels decreasing as they discharge, but this one is
    > consistently unusual.
    >
    > I'm using the Maha PowerEx MH-C9000 battery charger/analyzer.
    >
    > Thanks.


    Between the first minute and three hours later did you leave it open
    circuit ? then the voltage can go up slightly, and it is normal.

    M. Moorthi
    www.battery-consulting.com
    MuMu, Dec 14, 2008
    #11
  12. John Doe

    John Doe Guest

    MuMu <> wrote:

    ....

    > Between the first minute and three hours later did you leave it
    > open circuit ?


    Absolutely positively not. It's consistently discharging at 500
    milliamps the entire time. After doing another "Break-In and
    Analysis" and again discharging but with the two batteries in
    opposite battery charger/analyzer slots, the weird battery starts at
    about .96 V and slowly rises, hours later to about 1.10 or 1.15
    before it starts falling and finishes discharging.
    John Doe, Dec 14, 2008
    #12
  13. On Fri, 12 Dec 2008 06:09:53 -0800 (PST), Martin Brown
    <|||newspam|||@nezumi.demon.co.uk> wrote:
    >But there is something odd happens with matched sets of NiMH batteries
    >in some digicam applications. I have several sets for a Pentax istD
    >digicam. What I have noticed is that one cell always appears weaker
    >than all the others by a significant margin and the camera fails early
    >with "low battery" when NiMH cells are used ending up with 3 good ones
    >and one flat. The first one to go flat kills it. The odd thing is that
    >I suspect the flat is almost always in the same battery slot - as if
    >there is some extra burden on that specific cell. Using flash heavily
    >or excessive cold generally tips it over the edge more quickly.
    >
    >I have taken to putting dots on the failing cells but there is no
    >obvious pattern - it isn't same cell failing every time due to higher
    >self discharge or internal factors. I have noted the position where
    >the cell most likely to fail resides and swap it out on failure. This
    >usually works and has better odds than perm 4 from 8 with 2 duds.
    >
    >More curious still single use Duracells with higher terminal voltage
    >which I use when the NiMH have all died always seem to discharge
    >evenly. I would be interested if anyone can explain this.
    >
    >Regards,
    >Martin Brown


    I wonder what would happen if you put an alkaline in that slot, along
    with rechargables in other slots? The evil slot probably is powering
    something else as well.

    Regards,
    Bob Monsen
    Robert Monsen, Dec 14, 2008
    #13
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