Battery depletion oddness

Last night I was taking some long exposures. The battery level indicator
suggested the cells were partially depleted. At a certain point, the
camera told me the cells were wholly depleted and refused to take any
more. After turning the camer off and on again, they were back to being
partially depleted and I took several more shots. This morning the
indicator confidently reported that they were fully charged.

They are NiMH cells, and this isn't the first time I've had unexpected
behaviour from them. The camera is a Pentax K100D.

Is this unusual, or is it just how these cells behave under such
circumstances?

Daniele

On Wed, 1 Aug 2007 09:16:46 +0100, D.M. Procida wrote:

Last night I was taking some long exposures. The battery level indicator
suggested the cells were partially depleted. At a certain point, the
camera told me the cells were wholly depleted and refused to take any
more. After turning the camer off and on again, they were back to being
partially depleted and I took several more shots. This morning the
indicator confidently reported that they were fully charged.

They are NiMH cells, and this isn't the first time I've had unexpected
behaviour from them. The camera is a Pentax K100D.

Is this unusual, or is it just how these cells behave under such
circumstances?

That's not uncommon with many batteries, and is usually referred
to as a "voltage rebound" that occurs after the batteries are rested
for a while. But with NiMH batteries, if the camera is basing its
warning on the voltage level and it's reasonably accurate, then at
least one of the NiMH batteries (usually an AA cell or another type
of cell hidden inside a proprietary battery pack) is just about
completely discharged and you really should replace or recharge the
batteries as soon as possible, otherwise you risk shortening the
battery's life. Alkaline batteries on the other hand are notorious
for this, have a very pronounced voltage rebound. Depending on the
camera, you may be able to use the batteries for quite a long time
after this.

Here's an extreme example of this effect. When I first tested
alkaline AA batteries in a Fuji S5100 a couple of years ago, I
wanted to see if the battery life mentioned in the camera's manual
was accurate. So I duplicated what the manual referred to as a
standard test called the CIPA procedure. It had many requirements,
one of which was to take alternate shots with the flash used at full
power and with the flash not used. Recharging the flash uses a
*lot* of the battery's power and lowers their voltage by quite a bit
more than if the flash isn't used. The manual indicated that the
camera should be able to take 200 shots this way. I was able to
take nearly 200 shots when the battery warning came on
intermittently. Continuing, the camera was able to take about 220
shots before the voltage was so low that the camera powered off
automatically.

At that point, instead of replacing the alkaline AA batteries, I
stopped doing the CIPA test by not using the flash for any more
shots, and allowing the camera to have periodic rests. Over the
next couple of days those same batteries (due to rebound) were able
to take more than another 400 additional shots.

NiMH batteries aren't like this at all. They are rated in the
Fuji S5100 for 400 CIPA test shots, and if the battery warning came
on at that point, if would be a bad decision to keep using them,
even if the flash also wasn't used for additional shots, as their
voltage rebound is minimal since unlike alkaline batteries, at this
point they're almost completely depleted, and the NiMH batteries
could easily become damaged if you continue to use them. You can
easily see the effect of voltage rebound with a flashlight that has
"weak" alkaline batteries. If you continue using it, the light will
become dimmer and dimmer, until the bulb's filament is barely
emitting even a weak glow. Turn the flashlight off for 5 or 10
minutes, and it will be much brighter when you turn it on again.
But after a short period, it will die again. You should be able to
repeat this cycle many, many times before the batteries are totally
useless. But again, while you can do this with alkaline batteries,
it wouldn't be wise to treat NiMH batteries this way.

"D.M. Procida" wrote in
message
...
Last night I was taking some long exposures. The battery level indicator
suggested the cells were partially depleted. At a certain point, the
camera told me the cells were wholly depleted and refused to take any
more. After turning the camer off and on again, they were back to being
partially depleted and I took several more shots. This morning the
indicator confidently reported that they were fully charged.

They are NiMH cells, and this isn't the first time I've had unexpected
behaviour from them. The camera is a Pentax K100D.

Is this unusual, or is it just how these cells behave under such
circumstances?
Batteries indicating flat, then indicating higher charge after a rest, is a
fairly normal occurrence in cells that are subjected to fast discharge rates
(as happens in a digital camera). What happens internally is that the
chemical closest to the cell's anode & cathode becomes depleted, meaning a
drop in voltage, and hence showing as a low battery. After the device is
turned off, the chemical redistributes itself internally, and so the voltage
rises back to near that of a fully charged cell. Of course the cell is still
nearly flat, so you will only get a few shots before it will show flat
again.

This behaviour won't be observed when the cells are used in a device that
has a low current drain, as the slow discharge rate allows the chemistry to
deplete evenly.

The problem is more pronounced in cells that aren't designed for high
current drain. For example if you were to use "heavy duty" batteries, rather
than alkaline or NiMH, you would find that they will indicate flat after
only a handful of shots. Turn it off, let it rest for a while, and you will
get almost as many shots again. They will repeat this behaviour several
times before they are truly flat.

Daniele

"Doug Jewell" wrote in message
...

"D.M. Procida" wrote in
message
...
Last night I was taking some long exposures. The battery level indicator
suggested the cells were partially depleted. At a certain point, the
camera told me the cells were wholly depleted and refused to take any
more. After turning the camer off and on again, they were back to being
partially depleted and I took several more shots. This morning the
indicator confidently reported that they were fully charged.

They are NiMH cells, and this isn't the first time I've had unexpected
behaviour from them. The camera is a Pentax K100D.

Is this unusual, or is it just how these cells behave under such
circumstances?
Batteries indicating flat, then indicating higher charge after a rest, is
a fairly normal occurrence in cells that are subjected to fast discharge
rates (as happens in a digital camera). What happens internally is that
the chemical closest to the cell's anode & cathode becomes depleted,
meaning a drop in voltage, and hence showing as a low battery. After the
device is turned off, the chemical redistributes itself internally, and so
the voltage rises back to near that of a fully charged cell. Of course the
cell is still nearly flat, so you will only get a few shots before it will
show flat again.

This behaviour won't be observed when the cells are used in a device that
has a low current drain, as the slow discharge rate allows the chemistry
to deplete evenly.

The problem is more pronounced in cells that aren't designed for high
current drain. For example if you were to use "heavy duty" batteries,
rather than alkaline or NiMH, you would find that they will indicate flat
after only a handful of shots. Turn it off, let it rest for a while, and
you will get almost as many shots again. They will repeat this behaviour
several times before they are truly flat.

Daniele


My experience, YMMV:

I bought a Sony DSCH1, and one of the main reasons was it took AA batteries.
I then went out and bought about twenty rechargeable nimh batteries. I then
found out about "smart chargers", and bought one, a Sony that was on sale
where I got the camera.

In the ensuing time, my nimh's have been all over the board. Some last a
good while, some a medium time, and some seem to be dead right after a
charge. (The Sony brands.) I did a refresh on them yesterday, about an
eight hour process.

I use my camera a lot, on some days taking 1,000 vga size pictures on HOA
inspections. So, they get a workout. Still, when I pull them from the
"full" pouch, some indicate a full charge, some a half charge.

My next camera WILL be a Nikon D40x, and whatever the batteries cost, is
what they will cost. I purposely bought this one because one can always go
to the nearest store and get AA batteries if everything else runs out. (As
my friend's Nikon did in Mazatlan, and he didn't have an extra battery or
charger.) He's an idiot, but that's another story.

Nimh's are better than nicads. But they still have their idiosyncrasies.

Steve

They are NiMH cells, and this isn't the first time I've had unexpected
behaviour from them. The camera is a Pentax K100D.

Is this unusual, or is it just how these cells behave under such
circumstances?

In addition to the general issues that others have described, the Pentax
DSLR's in particular have an uneasy relationship with NiMH cells. The
problem is that their voltage is actually on the low side - 1.3-ish
rather than 1.5. So four of them come well shy of the 6 volts the
camera is hoping for. The camera is OK with that, to a point - the
voltage doesn't have to fall off very much in order to fall below the
threshold the camera requires. And as described, a bit of rest allow
the batteries to settle down and show more voltage.

There has been much discussion over whether some brands of NiMH AA's
will reliably show more voltage for longer than others, or whether there
is more variety *within* a given brand than *between* brands. The new
"Eneloop" and other cells that are designed to reduce the self-discharge
rate seem to be working very well for virtually everyone who has tried
them. While they ostensibly have less "juice" than many regular NiMH's
and would therefore drain faster if they were allowed to drain
completely, they seem to keep their charge above the magic threshold
that Pentax DSLR's require for longer.

---------------
Marc Sabatella


Music, art, & educational materials
Featuring "A Jazz Improvisation Primer"
http://www.outsideshore.com/

"SteveB" wrote in message
...



My experience, YMMV:

I bought a Sony DSCH1, and one of the main reasons was it took AA
batteries. I then went out and bought about twenty rechargeable nimh
batteries. I then found out about "smart chargers", and bought one, a
Sony that was on sale where I got the camera.

In the ensuing time, my nimh's have been all over the board. Some last a
good while, some a medium time, and some seem to be dead right after a
charge. (The Sony brands.) I did a refresh on them yesterday, about an
eight hour process.

I use my camera a lot, on some days taking 1,000 vga size pictures on HOA
inspections. So, they get a workout. Still, when I pull them from the
"full" pouch, some indicate a full charge, some a half charge.
How long between charge and use? NiMH batteries have a fairly rapid self
discharge pattern, and if they have been in your bag for a few weeks, it is
quite on the cards that they will be nearly flat. There are new batteries
that don't self-discharge as quick (brands include things like eneloop,
hybrio, elock), which may be better for you. These types of batteries have a
slightly lower capacity, but because of their low rate of self discharge,
you are more likely to get the rated capacity from them.
Also, all rechargeable batt's have a fairly limited life span - normally
18-24 months is about all you'll get before they significantly lose their
capacity.

My next camera WILL be a Nikon D40x, and whatever the batteries cost, is
what they will cost. I purposely bought this one because one can always
go to the nearest store and get AA batteries if everything else runs out.
(As my friend's Nikon did in Mazatlan, and he didn't have an extra battery
or charger.) He's an idiot, but that's another story.

Nimh's are better than nicads. But they still have their idiosyncrasies.

Steve

In article
,
"Doug Jewell" wrote:

"SteveB" wrote in message
...



My experience, YMMV:

I bought a Sony DSCH1, and one of the main reasons was it took AA
batteries. I then went out and bought about twenty rechargeable nimh
batteries. I then found out about "smart chargers", and bought one, a
Sony that was on sale where I got the camera.

In the ensuing time, my nimh's have been all over the board. Some last a
good while, some a medium time, and some seem to be dead right after a
charge. (The Sony brands.) I did a refresh on them yesterday, about an
eight hour process.

I use my camera a lot, on some days taking 1,000 vga size pictures on HOA
inspections. So, they get a workout. Still, when I pull them from the
"full" pouch, some indicate a full charge, some a half charge.
How long between charge and use? NiMH batteries have a fairly rapid self
discharge pattern, and if they have been in your bag for a few weeks, it is
quite on the cards that they will be nearly flat. There are new batteries
that don't self-discharge as quick (brands include things like eneloop,
hybrio, elock), which may be better for you. These types of batteries have a
slightly lower capacity, but because of their low rate of self discharge,
you are more likely to get the rated capacity from them.
Also, all rechargeable batt's have a fairly limited life span - normally
18-24 months is about all you'll get before they significantly lose their
capacity.

My next camera WILL be a Nikon D40x, and whatever the batteries cost, is
what they will cost. I purposely bought this one because one can always
go to the nearest store and get AA batteries if everything else runs out.
(As my friend's Nikon did in Mazatlan, and he didn't have an extra battery
or charger.) He's an idiot, but that's another story.

Nimh's are better than nicads. But they still have their idiosyncrasies.

Steve


You sure you have a smart charger? Does it take batteries individually
or only in pairs?

--
To reply no_ HPMarketing Corp.

ASAAR wrote:

Last night I was taking some long exposures. The battery level indicator
suggested the cells were partially depleted. At a certain point, the
camera told me the cells were wholly depleted and refused to take any
more. After turning the camer off and on again, they were back to being
partially depleted and I took several more shots. This morning the
indicator confidently reported that they were fully charged.

That's not uncommon with many batteries, and is usually referred
to as a "voltage rebound" that occurs after the batteries are rested
for a while. But with NiMH batteries, if the camera is basing its
warning on the voltage level and it's reasonably accurate, then at
least one of the NiMH batteries (usually an AA cell or another type
of cell hidden inside a proprietary battery pack) is just about
completely discharged and you really should replace or recharge the
batteries as soon as possible, otherwise you risk shortening the
battery's life.

I've continued using them since that happened the other night, with the
indicator still reading fully-charged.

So now I'm in a dilemma: keep using them when this happens, possibly
damaging one or more of the cells, or recharge batteries which are not
adequately discharged, possibly overcharging and damaging them.

Daniele

On Fri, 3 Aug 2007 16:37:34 +0100, D.M. Procida wrote:

So now I'm in a dilemma: keep using them when this happens, possibly
damaging one or more of the cells, or recharge batteries which are not
adequately discharged, possibly overcharging and damaging them.

That shouldn't be a problem if you have even a halfway decent
battery charger. The poorer ones charge batteries in pairs, and the
good ones have a charging circuit for each NiMH cell, so every
battery gets only as much charge as it needs. Both of these types
are known as "smart" chargers. The ones you'd really want to avoid
are much harder to find these days, and they're the ones that are
timer based. They tend to be very slow, and many of them would
charge for about 13 hours. At such a slow charge rate, overcharging
wouldn't be nearly as bad, since it wouldn't result in excessive
overheating, but a battery that only needed 3 hours of charging
would get the full 13 hours in one of those chargers. This wouldn't
be particularly good if repeated often. If your charger is more
than a couple of years old, the odds of it being timer based is much
greater, and if it really is one of those you really should consider
replacing it with something more modern. Smart chargers are fairly
inexpensive these days, and are widely available, not just in good
camera stores, but in convenience stores like Rite-Aid, CVS, etc.

With a "smart" charger you'd simply charge the batteries whenever
you have the time. If the batteries are only half depleted, no
problem. You'd be avoiding using them to the point of exhaustion,
which in most cases is much tougher on NiMH batteries than
overcharging, which shouldn't happen with smart chargers.