High-capacity NiMH cells -- very rapid self-discharge common?

I recently bought some cheap no-name (actually "Tenergy," whatever that is)
2600mAh AA cells on eBay. I haven't tried to assess the accuracy of their
rating, don't know how I'd do that anyway, but I'm flabbergasted by how fast
they self-discharge -- a couple days or so, sometimes almost overnight, it
seems. Tried leaving them on charge overnight, no difference. Tried
"conditioning" them in a Maha C204W, still no difference. Charged with a
Maha C401FS, individual charging circuits for each cell, still no
difference. So far they do not seem to improve with use either.

So I tried some more cheap no-name (really no-name this time, just cell info
on a pale green case) 2600mAh cells from a different eBay source. Pretty
much the same thing. From fully charged they go flat amazingly fast with no
use at all. Not actually zero-voltage flat, they'll still light a two-cell
flashlight, but flat enough that a couple of days after charging they won't
operate an old four-cell Minolta S404 for more than a few shots.

I've used no-name (or unheard-of name) NiMH cells from eBay sellers before,
with excellent and reliable results, and most of those cells are still
giving me good results after several years. But they were of lower capacity,
2000 mAh or less. So I'm wondering if fast self-discharge is a
characteristic of these newer 2600mAh NiMH cells in general, or if it's just
that cheap cells ain't what they used to be.

Neil

I have similar experiences with many NiMH cells and batteries.

I now use Eneloops for many applications.

"ransley" wrote in message
...


Have you put a V meter on them to see if they even charge and what the
discharge is. I can let them sit a month and still have use, but not
cheap no names. Try Eneloop are a different design, but measure what
voltage your chargers give, mine charge to 1.5v or so

________________

Good idea, I will check the charging voltages. But my Maha chargers are the
same ones I've been using with other NiMH cells for a long time, with no
problems.

As for discharge, I suppose I could get a suitable resistor from Radio
Shack, rig up a multitester somehow and plot the discharge curve -- but
that's really more tedious than I care to get into, unless there's a simpler
method that hasn't occurred to me. I used to do that 30+ years ago with NiCd
battery packs when I was flying R/C models.

Neil

"Charles" wrote in message
. ..


I have similar experiences with many NiMH cells and batteries.

I now use Eneloops for many applications.

Yep, Eneloops are probably the answer. Never used 'em before, but I just
ordered a 4-pack yesterday.

Neil

"Neil Harrington" wrote in message
. ..

"Charles" wrote in message
. ..


I have similar experiences with many NiMH cells and batteries.

I now use Eneloops for many applications.

Yep, Eneloops are probably the answer. Never used 'em before, but I just
ordered a 4-pack yesterday.

I'll predict that you will like them.

The mAH rating is highly overrated ;)

On Tue, 24 Jun 2008 17:36:35 -0400, Neil Harrington wrote:
I recently bought some cheap no-name (actually "Tenergy," whatever that is)
2600mAh AA cells on eBay. I haven't tried to assess the accuracy of their
rating, don't know how I'd do that anyway, but I'm flabbergasted by how fast
they self-discharge -- a couple days or so, sometimes almost overnight, it
seems.

Are they "2600mAh" cells, or "Up to 2600mAh" cells? :-)
A set of Panasonics I bought state "Up to 2100 mAh". They are working
ok for me -- so far. But, when they go dead, Dead, DEAD , they will
still meet Panasonic's 'specifications'.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http://jonz.net/ng.htm

Neil Harrington wrote:
"ransley" wrote in message
...


Have you put a V meter on them to see if they even charge and what the
discharge is. I can let them sit a month and still have use, but not
cheap no names. Try Eneloop are a different design, but measure what
voltage your chargers give, mine charge to 1.5v or so

________________

Good idea, I will check the charging voltages. But my Maha chargers are the
same ones I've been using with other NiMH cells for a long time, with no
problems.

As for discharge, I suppose I could get a suitable resistor from Radio
Shack, rig up a multitester somehow and plot the discharge curve -- but
that's really more tedious than I care to get into, unless there's a simpler
method that hasn't occurred to me. I used to do that 30+ years ago with NiCd
battery packs when I was flying R/C models.

Neil


The good folks over at CandlePowerForums
http://www.candlepowerforums.com/vb/...d.php?t=149804 have studied
this subject extensively. Might save yourself some time and energy in
reviewing what they did before doing any analysis yourself.

Clair

Clair Johnston wrote:
Neil Harrington wrote:

"ransley" wrote in message
...


Have you put a V meter on them to see if they even charge and what the
discharge is. I can let them sit a month and still have use, but not
cheap no names. Try Eneloop are a different design, but measure what
voltage your chargers give, mine charge to 1.5v or so

________________

Good idea, I will check the charging voltages. But my Maha chargers
are the same ones I've been using with other NiMH cells for a long
time, with no problems.

As for discharge, I suppose I could get a suitable resistor from Radio
Shack, rig up a multitester somehow and plot the discharge curve --
but that's really more tedious than I care to get into, unless there's
a simpler method that hasn't occurred to me. I used to do that 30+
years ago with NiCd battery packs when I was flying R/C models.

Neil

The good folks over at CandlePowerForums
http://www.candlepowerforums.com/vb/...d.php?t=149804 have studied
this subject extensively. Might save yourself some time and energy in
reviewing what they did before doing any analysis yourself.

Clair
Excellent forum on NiMh and self discharge rates. Thanks for the link.

"Allodoxaphobia" wrote in message
...
On Tue, 24 Jun 2008 17:36:35 -0400, Neil Harrington wrote:
I recently bought some cheap no-name (actually "Tenergy," whatever that
is)
2600mAh AA cells on eBay. I haven't tried to assess the accuracy of their
rating, don't know how I'd do that anyway, but I'm flabbergasted by how
fast
they self-discharge -- a couple days or so, sometimes almost overnight,
it
seems.

Are they "2600mAh" cells, or "Up to 2600mAh" cells? :-)

They claim to be 2600mAh. No "up to" is mentioned, but I'm inclined to take
such specs with a grain of salt anyway. :-)

Neil


A set of Panasonics I bought state "Up to 2100 mAh". They are working
ok for me -- so far. But, when they go dead, Dead, DEAD , they will
still meet Panasonic's 'specifications'.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http://jonz.net/ng.htm

"Clair Johnston" wrote in message
. ..
Neil Harrington wrote:
"ransley" wrote in message
...


Have you put a V meter on them to see if they even charge and what the
discharge is. I can let them sit a month and still have use, but not
cheap no names. Try Eneloop are a different design, but measure what
voltage your chargers give, mine charge to 1.5v or so

________________

Good idea, I will check the charging voltages. But my Maha chargers are
the same ones I've been using with other NiMH cells for a long time, with
no problems.

As for discharge, I suppose I could get a suitable resistor from Radio
Shack, rig up a multitester somehow and plot the discharge curve -- but
that's really more tedious than I care to get into, unless there's a
simpler method that hasn't occurred to me. I used to do that 30+ years
ago with NiCd battery packs when I was flying R/C models.

Neil
The good folks over at CandlePowerForums
http://www.candlepowerforums.com/vb/...d.php?t=149804 have studied
this subject extensively. Might save yourself some time and energy in
reviewing what they did before doing any analysis yourself.

Clair

Great site! Thanks very much for that; into my Favorites it goes right away.

Neil