Lostgallifreyan said:
A lot of NiMH troubles can be traced to microthicknesses of grime or
nonconductive salts on the terminals. I had some that looked like they were
decaying at different rates in charge retention, and I decided to try a bit
of brasso on their terminals and give them another go, and they behaved
equally again, camera use went from around an hour to around four hours.
That's a big recovery considering there didn't appear to be a problem with
terminals before cleaning. It doesn't take a lot for the charger to fail to
push enough current, it can drop well before the little LED's make the
failure obvious.
Fascinating - thanks for the report.
Some Caig Labs DeOxIt might be equally effective at getting off the
grime and restoring the contact quality.
Re alkalines, are any of them rechargeable? That's not a facetious
question, if there are any, I want some.
Rayovac used to make specialized rechargeable alkaline batteries. I
gather that these are discontinued (they never really caught on) but
that Pure Energy in Canada is making equivalents.
They do work, I understand, but aren't an ideal solution. They
apparently start out with a charge capacity similar to a standard
alkaline, but their capacity drops off somewhat each time they're
discharged and recharged. There seems to be an inverse relationship
between lifetime (in number of cycles) and depth of discharge - deep
discharge reduces the number of total cycles you can get before the
battery is degraded to the point where it's no longer useful. Also,
a specialized charger is required - a standard NiCd or NiMH charger
cannot be used.
Although Pure Energy states that their battery can be recharged up to
500 times, another report I've read suggests that 50 cycles at
half-discharge and 10 cycles at deep discharge can be expected, and
that a complete discharge can leave the cell in a non-rechargeable
state and thus kill it completely. Possibly the technology has
improved since the latter report was written in 2002, or possibly the
500-cycle number assumes a very shallow discharge.
Rechargeable alkalines also seem to have a relatively high internal
resistance, which limits their ability to deliver high amounts of
current (400 mA max for an AA cell is suggested by one writeup).
For most rechargeable applications, NiMH seems the best solution for
devices that you can keep "topped up" on a charger frequently, while
the older NiCd types may still be best for applications where you need
to charge the device and then stick it in a box and not think about it
for several months and then expect it to work reliably.