Photography - Battery question

On Sun, 23 Aug 2009 06:27:46 GMT, "David J Taylor"
wrote:

"David J Taylor"
wrote in
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Yes, NiCd and NiMH /do/ require different chargers.

David

.. or different settings on the same charger, if you have a dual-mode
charger.

David

True only on newer higher-amperage chargers, not true on older NiCd
chargers. If your old NiCd charger only puts out 80-150 mA, the type where
you timed how long you left a NiCd cell in the charger (the 12-18 hrs. to
charge variety) then you can use the same charger with NiMH cells, leaving
them in there as long as you wish, weeks, months even. They might lose a
little life expectancy but not so as you'd notice more than any other mild
charging abuse of NiMH cells. Granted charging times with the higher
capacity of today's NiMH cells will also increase the top-off charging time
up to twice as long (25-36 hrs.), but you *can* use your old NiCd chargers
with new NiMHs. If that's all you have and don't mind leaving them in the
charger indefinitely until you need them, there's no harm in using old
chargers with new cells, both kinds of cells.

If your old charger puts out 250-300mA (read the current on the device or
wall-transformer), you could probably get away with using that too. Just
don't leave the NiMH cells in them for many days and weeks. They'll be safe
with a constant current that high on them, but it will shorten their life
by being kept a little warmer with more possible out-gassing. (Why most
batteries die before their time: The liquid component(s) turn to gas when
over-heated. If the internal pressure is too high it vents this precious
gas to the atmosphere and it can't condense back into liquid inside the
battery again when the battery cools. In effect, they cyclically get dried
out.)

Anecdotal evidence to the contrary (and contrary to all other advice you'll
read):

A photo-trekking buddy back in 2003 (year important because standard NiMH
chemistry was still being tweaked back then) had an old wall-pack type 4-AA
NiCd fast-charger that output 400mA per cell. He would leave his NiMH cells
in that charger all the time until needed (on the 120v inverter in the
motor-home photo-rig or when our rig was plugged into services at a more
civilized campgrounds). I kept trying to convince him to use other newer
12v traveling NiMH chargers with auto-shutoff, etc. (like mine were),
concerned about him possibly damaging his batteries, or exploding and doing
worse damage. But he didn't care and didn't mind. As long as what he was
doing worked for him he kept doing it, there was no convincing him
otherwise. They were decidedly very very warm whenever I'd check them over
the days. Almost too hot to touch. After a day they were not too different
than the temperature that mine reach in a 2.5-3 hour charger at the end of
the charging cycle. Yet it didn't destroy the batteries as quickly as I
thought it would, if indeed it ever did.

Over a period of almost a year he was swapping-out batteries a little more
often than once a week, always returning the old set to the same charger. I
being concerned they'd burst into flames or eventually explode one day.
None of the cells being kept with that high of a current on them for many
days (for weeks a couple times) seemed to be diminished in capacity during
that year. I suspect that (some?) NiMH cells are much more forgiving than
we want to believe. I wouldn't recommend using that high of a current on
NiMHs indefinitely, but I also wouldn't be overly concerned if I left them
in a charger of that type for that long because I had forgot about them.
Not after seeing how well his sets of batteries survived that kind of
charging abuse. This was even before they improved on the NiMH chemistry
used today. You'd probably end up buying a new set just for the hell of it
because you saw some on sale before you could ever kill the old ones with a
constant 400mA current, according to what I've witnessed.