Re: Battery woes

On Tue, 12 Jun 2007 18:54:19 GMT, Thomas T. Veldhouse wrote:

I should have said that it's not possible inside the camera. Or perhaps
more accurately, it's too expensive to implement the pulse load test
inside the camera, especially considering the manufacturers are cutting
every possible expense on the AA powered cameras in the first place.

It's an inherent characteristic of NiMH batteries that the voltage
discharge curve is so flat. This isn't necessarily a bad thing, but it
does mean that it's non-trivial to measure remaining capacity, and it
results in the lack of accurate battery level indicator in-camera for AA
powered cameras.

You can get reasonably accurate capacity readings based on voltage alone, but
it doesn't work well when the battery becomes damaged [or nears end-of-life].
The MB-D200 grip for the Nikon D200 takes any AA battery and of course the
standard LiIon batteries. The D200 can be configured to know that it is using
NiMH batteries and does a good job with it.

It's strange that so many smart chargers are available, often for
under $15, yet they manage to have the complex pulse/delta v charge
circuitry, yet cameras that cost hundreds of dollars can't also
incorporate similar inexpensive, albeit moderately complex circuits.
And again, my PDAs and radios didn't need anything more
sophisticated than a fairly accurate voltmeter to track the battery
charge state. This even with the relatively flat discharge curve of
NiCd and NiMH batteries. Why? Because while the voltage curve is
relatively flat, it's not horizontal. It has a fairly uniform slope
and battery capacity tracks very well with voltage at a given load.
NiMH batteries are flat and need to be recharged when the voltage
drops to a little above 1.00 volts per cell. When fully charged,
the voltage will be up around 1.25 volts, and it drops pretty
uniformly and is easily monitored by the simplest camera CPU. As
usual, SMS is spreading his misinformation/disinformation about what
is and what isn't possible. He's been doing it for years.

.

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