"Jeff Liebermann" wrote in message
...

NiMH cells do NOT totally discharge themselves. They discharge to
about 50% of capacity (by self-discharge) and then just sit there.

Then what is the problem? A 50% loss of capacity is hardly disastrous.


For example, here are some curves I ran for an Energizer 2300ma-hr
cell:
http://802.11junk.com/jeffl/NiMH/Energizer-NiMH-2300.jpg
and for an Duracell 2050ma-hr cell:
http://802.11junk.com/jeffl/NiMH/Duracelll-NiMH-2050.jpg
There were brand new cells used to test the assertion that NiMH cells
need to be charge cycled a few times before they reach full capacity.
Basically, that's true.

Note the voltages (under 1C load). For the Energizer, it starts off
at 1.35v and starts to die at about 1.10v. If you put a load on your
Sanyo cells, I'm fairly sure your 1.23v no load voltage will drop to
something around 1.18v. In other words, your Sanyo batteries
self-discharged until they were almost dead, and stopped.

But they weren't "almost dead".

This morning, I did what I should have done before I posted. Over a period
of a half-hour, I fired the Canon 580EX II over 100 times AT FULL POWER. The
recycling time was 3 to 3.5 seconds (not unreasonable for full-power
recycling), and the final cell voltage was about 1.21V (before the cells had
time to recover).

100 full-power flashes is not "almost dead". Had I fired on automatic, at a
moderate aperture, not using full power, I could easily have gotten 200 or
300 flashes. And had I been willing to tolerate a 5-second recycle, I
probably could have gotten another 100 full-power flashes.


I recently had a similar experience to what you found. I have two old
Norelco rotary shavers. I received both with dead batteries and
replaced them with NiMH cells of dubious origin. I only charge them
when needed, except this time, when a dry squall dropped a few trees
through the power lines.
http://802.11junk.com/jeffl/pics/2011-12-03-Storm/
When I dug out the shavers, the LCD indicator showed a nearly full
charge (about 80%). However, when I tried to use it, both lasted less
than 60 seconds. My guess(tm) is that I hadn't charged it since last
winter (9 months).
That's fairly close to what you observed. There was sufficient
voltage for the LCD indicator to proclaim a nearly full charge, but
not enough stored energy to do much useful work.

That isn't what I observed this morning. The cells, which had sat for almost
two years since being fully charged, were perfectly usable for 100
full-power flashes. I probably have gotten another 100 flashes, but I didn't
want to take the chance of abusing the flash.

The cells are Sanyo Superlattice Alloy EVO, model HR-3U. They were not
shipped pre-charged, and as far as I can tell, they are not
slow-self-discharge ("eneloop") cells. The Sanyo USA site has no information
about them. However, they are available from Batteries America. (Thomas
Distributing doesn't list them.)