I found the following interesting data in an electronic component catalogue:

	      Voltage    Capacity       Lifecycles      Weight     

Alkaline 	1.5V	2300-2700mAh	  -		 27gr

Carbon-Zinc 	1.5V	 500-1100mAh 	  -		  ?

NiCd 		1.2V	 500-1100mAh	1000 cycles 	 23gr

NiMH 		1.2V	1000-1200mAh	 500 cycles	 25gr

Lithium	      1.7-1.9V	3000mAh		  - 	         20gr 

Non-rechargeable
Alkali-Manganese
		1.5V	2800mAh		  -		  ?

Rechargeable 	
Alkali-Manganese
		1.5V	1000mAh		 100 cycles	  ?

Rechargeable 
Lithium-Ion	?	 ?		 400 cycles	  ?
(Sony)

Lithium CR123A	3.0V	1300mAh		  -		  ?

Lithium 2CR5	6.0V	1300mAh		  -		 39gr 

Lithium CRP2P	6.0V	1300mAh		  -		  ?

							   Nominal	Peak 
		 	Nominal	     After	 After	    peak 	after 		
		        capacity    3 cycles    8 cycles   current     5 cycles
NiMH			1100mAh	    1100mAh	1100mAh	    12A		 12A(assumed)
(Varta Accuplus)

Alkali-Manganese	1900mAh	      -		  -	     3.8A	  -
single-use
(Ucar Energizer)

Alkali-Manganese	1500mAh	    1300mAh	 850mAh	     3.8A	  2.0A
(BIG Alkaline)

Alkali-Manganese	1800mAh	    1050mAh	 650mAh	     3.8A	  1.9A
(Leclanche Boomerang)

NiMH has a higher internal resistance than NiCd; 'Not capable of high currents' as stated in this electronic components catalogue....
A typical NiMH AA-cell is capable of 3.6A continous, or 6A peak [the ColorFoto data suggests improvement on this spec]. I couldn't find NiCd data in AA size, but by comparing with a 1700mAh C-cell (40A continuous, 70A peak), one can safely assume that a 900mAh NiCd is capable of at least 10A/17A, if not 20A/35A! You can weld wires with NiCd's!
So, for high current applications like in flashes, NiCd works best in the field of rechargeables.

Beyond that, the self discharge of NiMH is a staggering 12-15% each day....NiCd does 1% each day....not a problem in cellular phones and lap tops, stuff that is likely to be hooked on to 110/22V every day....but a large problem with infrequently used photo gear.

As for the environmental arguments: NiMH is often claimed to be more friendly than NiCd, but one has to take into account that NiCd's can be recycled better....so it all comes down to the choice between resource depletion (NiMH) or toxic content (NiCd)....

Note that the sealed NiCd packs used by camera and flash manufacturers contain a matched set of batteries, they were selected for having an almost identical internal resistance. Different restances within a pack means that the cell with the least resistance is drained most, and will be empty first, long before the others are empty! By draining the set further, reverse polarisation of the least-resistance cell can occur! Throw such a set into a non-regulated charger, and you will have to replace all batteries very soon, because overcharging is the pest for NiCd's (often mistaken for memory effect!).

A few interesting messages in rec.photo.*

FROM: lmairs@clark.net (Lee Mairs)
SUBJECT: Re: NiCd memory effect? (was Canon PowerShot 600 question)
DATE: 4 Jun 1997 14:12:21 GMT
ORGANIZATION: SAG Corporation

>> Their conclusion was that modern NiCd batteries have virtually no memory
>> effect in practical usage. When they drained a NiCd battery 100 times 
>
>Then I sure would like to know why my $70 high capacity (2400mAhr) SONY
>nicad pak for my camcorder exhibited the memory effect over a period of
>2 years.
>Now it has 5 minutes of capacity.

I've been following this issue for some time, and it is 
indeed confusing.  NASA originally reported the "memory 
effect"; however, one of my students informed me that 
NASA no longer beleives there is a memory effect.  I 
sure seem to find it with my hand-held radios tho.  My 
Canon PS600 seem incredibly strong - much more so that 
I'd expected.  I bought 3 so I could use each one to 
parade rest to prevent memory effect.  So far I've only 
had to recharge once - the darn thing gets charged 
enough while I'm downloading pitures. 
Lee Mairs
Security Marine Services

FROM: hargravep@mala.bc.ca (Powell Hargrave)
SUBJECT: Re: NiCd memory effect-FAQ (long)
DATE: Sun, 01 Jun 1997 21:16:20 GMT
ORGANIZATION: Malaspina University-College

Alan Bredon  wrote:

>Could it be that the MEMORY EFFECT is *not* just an idea carried over
>from past experience with old technology NiCds ?
>
>Could it be that the manufacturers are lying when they say that "modern"
>NiCds don't exhibit the memory effect???


This is from a battery FAQ I saved some time ago.  Sorry I didn't keep
the address.  Should be able to find it with a search.

============================================================================

Q8.43: Can I bring my NiCd batteries from the dead?

NiCd cells which have developed internal short circuits can
sometimes be "zapped" back to life by a high-current pulse, which
burns out the metal whiskers which caused the short. This is
usually done by charging a good- sized capacitor up to 5 volts or
so (from a DC power supply, through a series resistor), and then
"sparking" the NiCd cell from the capacitor... the sudden current
surge will vaporize the whiskers. The cells should be removed
from the battery [pack] before this is done... don't try to "zap"
the cells while they're still connected to one another or to any
other equipment.

============================================================================

Q8.42: How SHOULD I care for/charge my NiCd batteries?

Don't overcharge it... don't leave it cooking in the charger for
days at a time... and don't overdischarge it by running it down
with an external resistor or light-bulb or LED.

============================================================================

Q8.41: Do NiCd batteries have "memory"?

[Definition: a "cell" is a single 1.2-volt device. A "battery" is
two or more cells wired up in series, giving a multiple of 1.2
volts.]

Nickel-cadmium batteries should NOT be completely discharged. To
do so runs a serious risk of damage to the battery. 

According to what I've read, in battery-manufacturer literature,
it is safe to discharge _individual_ cells all the way down to
zero. It's usually unnecessary to do so, but it can be
advantageous in some occasional cases... a full discharge of a
cell to zero will cure "voltage depression", which can occur if a
cell or battery is overcharged (left in the charger for too
long). 

It is NOT safe to discharge a battery of NiCd cells. The reason
is that one of the cells will probably run down before the others
do, and the "live" cells will continue to force current through
the exhausted cell. This leads to a condition known as
over-discharge... it's just as if you had inserted an exhausted
NiCd cell into a battery charger with "+" and "-" reversed.
Overdischarging a NiCd cell will damage it... the cell develops
internal short-circuits which will cause it to run down
prematurely in the future, and eventually the cell will no longer
take or hold a charge at all. 

Healthy NiCd cells have a voltage-vs.-charge-level curve which is
quite flat. They deliver very close to 1.2 volts per cell until
almost all of their charge has been exhausted... then the voltage
level drops off very quickly. By the time the cell voltage drops
to 1.1 volts per cell, only a few percent of the original charge
level remains. At least one manufacturer (Gates) states that the
battery should be considered to be exhausted when this voltage
level is reached... the small amount of power remaining in the
battery cannot be extracted safely, without running the risk of
overdischarging one of the cells and damaging it. 

Most well-designed camcorders (and, I infer, the PowerBooks)
includes power-management hardware which monitors the battery
voltage. When the voltage drops to 1.1 volts per cell, the
battery is considered to be exhausted and the machine shuts down.

> Will regular partial discharges with complete recharges limit
> the charge-life of the battery? 

No. There is something known as the "memory effect", which can
limit NiCd battery capacity if the battery is _repeatedly_
discharged to _exactly_ the same partial-discharge level, and
then fully recharged, many times in a row. Gates[1] states that
the memory effect is almost never seen in practice, because it
only occurs if the partial-discharge level is repeated very
precisely many times in a row. 

There _is_ an effect which can mimic the "memory effect", in the
sense that it makes the battery look as if it is losing capacity.
This effect, known as "voltage depression", occurs if you
over-charge a battery. The battery's output voltage drops from
1.2 to about 1.05 volts partway through the discharge cycle, and
this may "spoof" a power-monitoring circuit into believing that
the battery is exhausted. 

Voltage depression is curable. It can be cured by fully
discharging each cell of the battery... INDIVIDUALLY... all the
way to zero, and then recharging the battery. You can do this if
the battery design allows you to access the individual cells. You
can't do it if you can't get to the individual cells, but only to
the battery terminals. 

Alternatively, you can discharge the entire battery until the
total voltage drops to 1.0 volts per cell, and then recharge
it... do NOT try to discharge the battery all the way to zero, or
you will very probably damage it. This 1.0-volt-per-cell shutoff
should be safe (in particular, it leaves a good safely margin for
any battery rated at a nominal output voltage of 6.0 or less) and
should discharge all of the cells well past the
voltage-depression point. 

You can avoid overcharging by taking the batteries out of the
charger when they've been fully charged. If you need to keep NiCd
batteries in a "floating" application... if they must be be kept
constantly "topped up" to full charge without human
intervention... then you should use a charger which is
intelligent enough to switch to a low-rate trickle charge once
the battery is full. I believe that a trickle-charge rate of
about C/100 or so (e.g. 10 milliampere, for a
1000-milliampere-hour battery) is in the right ballpark - it will
compensate for the battery's rate of self-discharge. 

> (I don't want to have to completely discharge the battery every
> time I use it if I can help it!) 

You do not need to. If you have a habit of leaving your battery
cooking in the charger for longer than it needs, you might be
nudging it into voltage depression. If so, then you might want to
reset the battery every couple of months, by leaving it in the
PowerBook (with the PowerBook turned on and sleep-mode disabled)
until the PowerBook battery manager shuts the machine down due to
a low-voltage condition. You shouldn't need to do this more than
every few months, if at all. 

My understanding is that the total useful life of a NiCd depends
to some extent on how deeply the cell/battery is discharged
during each cycle. A NiCd might be good for 1000 partial
discharges (say, from 100% down to 75%), but for only 500 or less
complete discharges (down to the 1.0 volt per cell, 98% discharge
level). Therefore: if you deliberately deep-discharge your NiCd
cells every time you recharge them, you are actually _wasting_ an
appreciable fraction of their use life... it's counterproductive.

"Among the many users of batteries in both the industrial and
consumer sectors, the idea of a memory phenomenon in
nickel-cadmium batteries has been widely misused and understood.
The term 'memory' has become a catch-all 'buzzword' that is used
to describe a raft of application problems, being most often
confused with simple voltage depression. 

To the well informed, however, 'memory' is a term applied to a
specific phenomenon encountered VERY INFREQUENTLY [emphasis mine
- RLM] in field applications. Specifically, the term 'memory'
came from an aerospace nickel-cadmium application in which the
cells were repeatedly discharged to 25% of available capacity
(plus or minus 1%) by exacting computer control, then recharged
to 100% capacity WITHOUT OVERCHARGE [emphasis in the original].
This long term, repetitive cycle regime, with no provisions for
overcharge, resulted in a loss of capacity beyond the 25%
discharge point. Hence the birth of a "memory" phenomenon,
whereby nickel-cadmium batteries purportedly lose capacity if
repeatedly discharged to a specific level of capacity. 

The 'memory' phenomenon observed in this original aerospace
application was eliminated by simply reprogramming the computer
to allow for overcharging. [Note that no mention is made of
adding an intentional *discharge* to clear the problem - RLM] In
fact, 'memory' is always a completely reversible condition; even
in those rare cases where 'memory' cannot be avoided, it can
easily be erased. Unfortunately, the idea of memory-related loss
of capacity has been with us since. Realistically, however, '
memory' cannot exist if any one of the following conditions
holds: 

A. Batteries achieve full overcharge.
B. Discharge is not exactly the same each cycle
 - plus or minus 2-3%
C. Discharge is to less than 1.0 volt per cell.

Remember, the existence of any ONE of these conditions eliminates
the possibility of 'memory'. GE has not verified true 'memory' in
any field application with the single exception of the satellite
application noted above. Lack of empirical evidence
notwithstanding, 'memory' is still blamed regularly for poor
battery performance that is caused by a number of simple,
correctable application problems." 

[End of quote from GE tech. note]

This note goes on to list the following as the most common causes
of application problems wrongly attributed to 'memory': 

1. Cutoff voltage too high - basically, since NiCds have such a
flat voltage vs. discharge characteristic, using voltage sensing
to determine when the battery is nearly empty can be tricky; an
improper setting coupled with a slight voltage depression can
cause many products to call a battery "dead" even when nearly the
full capacity remains usable (albeit at a slightly reduced
voltage). 

2. High temperature conditions - NiCds suffer under high-temp
conditions; such environments reduce both the charge that will be
accepted by the cells when charging, and the voltage across the
battery when charged (and the latter, of course, ties back into
the above problem). 

3. Voltage depression due to long-term overcharge -
Self-explanatory. NiCds can drop 0.1-0.15 V/cell if exposed to a
long-term (i.e., a period of months) overcharge. Such an
overcharge is not unheard-of in consumer gear, esp. if the user
gets in the habit of leaving the unit in a charger of simplistic
design (but which was intended to provide enough current for a
relatively rapid charge). As a precaution, I do NOT leave any of
my NiCd gear on a charger longer than the recommended time UNLESS
the charger is specifically designed for long-term "trickle
charging", and explictly identified as such by the manufacturer. 

- Operation below 0 deg. C
- High discharge rates (above 5C) in a battery not specifically
designed for such use
- Inadequate charging time or a defective charger
- One or more defective or worn-out cells (NiCds DO have a finite
life; they won't keep charging and discharging FOREVER no matter
how well we baby them.) 

To close with one more quote from the GE note:

"To recap, we can say that true 'memory' is exceedingly rare.
When we see poor battery performance attributed to 'memory', it
is almost always certain to be a correctable application problem.
Of the...problems noted above, Voltage Depression is the one most
often mistaken for 'memory'..... 

This information should dispel many of the myths that exaggerate
the idea of a 'memory' phenomenon." 

Long-term continuous overcharging produces an artificially
induced drop in capacity that resembles memory. It can also
decrease the overall life of the cell. A deep discharge/charge
cycle will recover much of the cell's life but long-term damage
is very likely. This is not "true" memory because the cell is not
subjected to repeated charge/discharge cycles that the cell
eventually remembers. It's simply a decrease in capacity due to
overcharging, and yes, it is mostly reversible. It is also not
memory because the point at which the cell capacity drops out
varies with the rate of discharge. The capacity loss due to
long-term continuous overcharg- ing is caused by loss of contact
of the cadmium hydroxide particles with the negative plate.
Electron microscope pictures show that overcharging causes the
particles to grow larger, especially at higher temperatures. This
reduces the surface contact with the pores of the negative plate.
A deep discharge/charge cycle restores the hydroxide particules
to their normally smaller size -- increasing surface contact.
Overcharging on the negative plate occurs when all the cadmium
hydroxide is converted to cadmium metal. Once that occurs, only
hydrogen gas and heat are produced (Oxygen gas is produced at the
positive plate at the point that it becomes overcharged.) These
gases, especially hydrogen, will eventually vent from the cell if
overcharging continues, thus reducing the effectiveness of the
electrolyte. 

The real meaning of memory effect comes from precisely repeated
charge/ discharges (without overcharging) of sintered-plate
nickel-cadmium cells where the cell seems to remember the point
of discharge depth. The effect is exceedingly difficult to
reproduce, especially in lower ampere-hour cells. In one
particular test program -- especially designed to induce memory
-- no effect was found after more than 700 precisely-controlled
charge/discharge cycles. In the program, spirally- wound
one-ampere-hour cells were used. In a follow-up program,
20-ampere-hour aerospace-type cells were used on a similar test
regime. Memory effects showed up after a few hundred cycles.
[Test program conducted by Pensabene and Gould at GE, I believe.]
This kind of memory appears to be related to the "efficiency" of
the positive plate. It seems that repeated precise charge cycles
affects the ability of the cell's active chemicals to charge
fully, after which the positive plate begins to produce oxygen
(as if being overcharged). Hence, it is possible for both gases
and uncharged particules to exist simultaneously. Strangely, if
the cell is carried out into overcharge the memory effect largely
disappears. Hence, overcharging actually reverses the "true"
memory effect. 

Another reason memory effect is a myth since all the consumer
charger's I've seen actually overcharge until there is a slight
voltage drop (due to an increase in resistance from the formation
of larger cadmium hydroxide particules that cause contact loss).
It's because consumer chargers actually overcharge that you have
to give the battery a deep discharge from time to time. It has
nothing to do with memory. 

And just in case you are wondering what a sintered-plate is, the
plate is constructed by sintering [welding without melting] a
fine nickel powder with a surface area of about one square meter
per gram. This produces a honeycombed structure that is about 80%
open pores. The negative plate is then impregnated with cadimum
hydroxide. The positive plate is impregnated with nickelous
hydroxide (which converts to nickelic hydroxide when charged). 


================================================================
Powell Hargrave           Canon PowerShot 600 photo page at:
hargravep@mala.bc.ca      http://www.mala.bc.ca/~nag/photos.htm
================================================================

Date: Fri, 10 Oct 1997 9:08:25 +1200
From: Anthony Newland 
To: Nikon-Digest
Subject: Self-discharge rates for NiCds

Greetings

Just wanted to make a minor correction to the comment made on 
self-discharge rates for NiCds:
The self-discharge rate for NiCds is typically 1%/day  compared to 
~3%/day for NiMH and 0.02%/day for alkalines.

As was correctly stated, the charge capacity doesn't directly relate 
to life in a high drain device such as the F5 or F90X. In fact, the 
high capacity NiCds (>800mAh) use a sponge electrode to achieve the 
greater charge capacity instead of the more traditional sintered 
electrode found in the lower capacity cells (~500-600mAh).  At high 
currents, the batteries with a sponge electrode actually have a 
significantly reduced capacity since the capacity rating is usually 
based on a "moderate" current drain (whatever the manufacturer 
chooses that to be). 

I would advise caution to anyone wanting to use high capacity NiCds 
in the SB26 - speaking from personal experience. I have had several 
sets of 1000mAh NiCds leak and show signs of overheating (the waxy 
sleeves had discoloured) when used in rapid firing situations. 

Regards
Anthony
newlanda@fphcare.fp.co.nz

FROM: REMOVEschuster@REMOVEpanix.com (Mike "NO UCE" Schuster)
SUBJECT: Re: Rechargers for NiMH batteries
DATE: 18 Jan 1998 23:03:48 GMT
ORGANIZATION: PANIX Public Access Internet and UNIX, NYC

In article <69t5s2$fi8$10@news.a1.nl>,
Willem-Jan Markerink  wrote:
>In article <69oc1v$8el@news1.panix.com>,
>   REMOVEschuster@REMOVEpanix.com (Mike "NO UCE" Schuster) wrote:
>>>BTW. The RS 1hr charger does use delta-V although it would be nice if
>>>they came right out and said it.  They describe it in a round-about
>>>way.  They also need to address the issue of temp sensing.
>>
>>Yes it does seem to use delta-V, but there is a big danger in using
>>delta-V termination when you can stuff it with random cells that have not
>>been charged and discharged together; i.e. so they all enter the charger
>>more or less "alike". Since it is wired to charge (and monitor) them in
>>series, differences between cells are not accounted for, and I often find
>>that one cell out of the 4 may get MUCH hotter than the rest. This is the
>>folly of charging individual cells in series. It should at least use a
>>thermal cutoff but RS is too cheap to do that. 
>
>Interesting point.
>I also recently read that not all brands & types of NiCd cells show a 
>distinctive delta-V peak....sometimes even showing very different 
>behaviour....not sure if this is valid for NiMH as well, but it makes temp 
>sensors absolutely necessary in case of rapid-chargers.

True. 

NiMH cells do "peak" during charging, but its magnitude is 4 times
flatter than a nicad. This is why rapid charge circuits designed for
nicads don't do well with NiMH cells. Further, the peak is blunted even
more when you're looking at the sum voltage of 4 cells wired in series and
one is weaker than the rest ....


-- 
Mike Schuster      		|	70346.1745 at CompuServe dot COM
schuster at panix dot com	|	schuster at pol dot net 

FROM: gknox@mindspring.com
SUBJECT: Re: Using NiCd setting for NiMH in 5-hour Radio Shack charger
DATE: Thu, 19 Feb 1998 00:10:45 GMT
ORGANIZATION: MindSpring Enterprises

On Wed, 18 Feb 1998 16:02:55 -0500, "Josef Faulkner"
 wrote:

>Has anyone tried charging their NiMH AA's in the 5-hour Radio Shack charger
>using the NiCd setting instead?  I take it that this charger is dumb anyway
>since it uses a timer to charge the batteries.  The manual says that it
>charges NiCd AA's at 180mAh, where it charges NiMH at 305mAh.  I figure that
>since the timer shuts off at around 8 hours, this should be more accurate to
>the time it takes to charge 1200mAh AA's.
>
>So the question here is, does anyone know of any problems that I might
>encounter by doing this?  Does the charger actually do anything other than
>just change the charging power when you switch to/from NiCd to NiMH?
>
>Thanks for your responses.
>
>--
>Josef Faulkner -=- panther at gate dot net
>

Josef,

I have this same charger and batteries and had similiar questions
regarding the charging algorithm. I measured the actual charge current
for both the NI-CD and NI-MH position of the selector switch. With
NI-CD selected the current was 185 ma. With NI-Mh selected the current
was 290 ma. and this current was delivered regardless of the charge
state. I measured it at both the beginning of the charge cycle and
after 5 hours when the batteries were very warm. I did not however
investigate the current as a function of time in NI-CD mode since if
it did change it would be as a function of some charge state dependent
variable peculiar to NI-CDs and I didn't want to subject my new NI-MH
batteries to some innapropriate charge schedule. 

Therefore I resorted to opening the charger and taking a look at the
circuitry. The circuit appears to be way too complicated for a unit
that only charges at a constant current for a preset time and then
quits. There were two or three ICs and numerous discrete components. I
don't know how the thing determines when 8 hours are up but it
wouldn't take that much to do it. My conclusion therefore is that it
might be using something more sophisticated than constant current over
a preset time for the NI-CD setting (doubtful) but is surely using the
constant current method for the NI-MH batteries. This makes sense if
you consider the voltage-time curves during recharging for the two
battery types. I had a friend of mine who's an engineer for Linear
Technology Corp. (among other things they make battery charging ICs)
send me some literature concerning these issues. When a NiCd cell is
charged it reaches a pronounced peak voltage near the end of the
charge cycle. NiMH cells on the other hand exhibit a much more subtle,
thus harder to determine, voltage peak. I suspect this is why the
Radio Shack 5 hour charger charges NiMH batteries at a constant
current for a constant time. It's easier.

The recommended charging methods for both NiCds and NiMH though
similiar, are not the same; NiCd batteries can be charged at a C/10
rate indefinetly without damage, and this is the recommended charge
technique. NiMH on the other hand are also normally charged at the
C/10 rate but NiMH are more susceptible to damage than NiCd cells.
They can be charged at this rate for about 16 hours but then the
charge must be terminated or reduced to C/40 which may be maintained
indefinitely. Note that neither of these methods requires a charge
termination technique beyond timing. If however you want to Fast
Charge them you generally must use some form of charge termination
technique to actually determine the state of charge or you may damage
the cell. Fast Charge rates are typically >1C for <3hr. With the RS 5
hour charger the charging currents are such that it would not be
considered fast charge unless the cells being charged had capacities
of less than .185 Amp-Hrs for NiCds or about .3 Amp-Hrs for NiMH
cells. These are pretty small AA cells so I suspect that RS did not
intend this to be a Fast Charge device, and so probably did not put in
any charge termination method other than the timer.

In practice the charger is charging at about a C/4 rate if you charge
1200 mAh NiMH cells and the charger is in the NI-MH mode. This is
neither Fast Charge nor the recommended C/10 rate but somewhere in
between. At the rate it charges, completely depleted 1200 mAh NiMH
cells should require about 6.5 hours to fully charge. Note that
because the batteries are not 100% efficient in converting charge
current to stored charge you must deliver more energy during charging
than you will get out. The charger shuts down in 8 hours so you will
be charging for 1.5 hours more than required for a full charge if you
let the charger terminate on its own. This "probably" won't harm the
batteries too much... but. There's always a but in engineering. Most
digicams (at least my Oly 500L) do not actually deplete the batteries
before the camera quits working. I don't know how much of the usable
energy is actually extracted, but I bet it's only about 50% or so.
This means you will probably significantly overcharge your batteries
if you pop them in the charger and let them charge for 8 hours. You
have probably noticed that some chargers discharge the battery first,
ostensibly to ward off the dreaded memory effect, but actually to set
the battery to a known state of discharge so that charging can be
terminated via timer without damage to the battery. Wish I'd thought
all this out before I bought the charger!

Anyway, it happens that as the battery nears full charge there is a
pronounced increase in its temperature. This is quite noticeable just
by feel. I let them charge for a couple of hours then check their temp
every 1/2 hour or so. When they start to feel really warm, they're
charged.

You could also just discharge them completely (put them in a penlight
or something or discharge them through a ~4 ohm 1 watt resistor for a
while) then charge them for the full 8 hours. 

If in fact the NiCd setting charges at constant current for 8 hours
(probably) a completely depleted 1200 mAh NiMH cell would only be
about 80% charged at the end of the charge cycle. 


Greg Knox

FROM: davem@cs.ubc.ca (Dave Martindale)
SUBJECT: Re: Lithium Double AA Questions
DATE: 27 May 1998 10:34:55 -0700
ORGANIZATION: Computer Science, University of B.C., Vancouver, B.C., Canada
NEWSGROUPS: rec.photo.digital

"David W. Swager"  writes:
>In general, are Lithium Ion batteries rechargable?  If yes, anybody
>make AA size?  Charger recomendations?

Lithium Ion battery chemistry gives about 3.5-4 V per cell, which is just
not compatible with the 1.2-1.5 V per cell of NiCd, NiMH, carbon-zinc,
and alkaline batteries.  There will never be a Lithium Ion battery that
is a drop-in AA cell.

Someone *could* make a single LiIon cell that was the size of two AA
cells stacked end-to-end - that would work.  But it wouldn't fit in
many devices that have side-by-side battery holders.

LiIon cells are rechargeable, but they need special charging circuitry.
Charge them too much and you get metallic lithium in the battery, which
can start a fire.  Let them discharge too much and they are permanently
damaged.  The charge/discharge circuitry has to monitor each cell
individually, not just the battery pack as a whole.

For these reasons, LiIon batteries are always designed into a complete
system of charger, battery, and load electronics.  They are not used
as loose cells.

	Dave

FROM: "Michael K. Davis" 
SUBJECT: Alkaline AA vs. Lithium AA
DATE: 4 Oct 1998 16:47:59 GMT
ORGANIZATION: Primenet (602)416-7000
NEWSGROUPS: rec.photo.equipment.35mm

I just read a discussion of which Alkaline AA's are best and decided to
open a new thread to show why Lithium AA's are better than Alkaline
AA's -- when the current drain is high enough.

Take a look at this Excel 5.0+ spreadsheet:

http://www.smu.edu/~rmonagha/bronbatt.xls

It plots the relationship between current drain and battery capacity,
showing how much longer 1.5 Volt Lithium AA batteries last relative to 1.5
Volt Alkalines as the load increases.

If you don't have Excel (Mac or PC), here is the data without the plotted
points and trendline curve:

Energizer. AA Alkalines (E91 Zn/Mn02)                   
vs. Energizer. AA Lithiums (L91 Li/FeS2)                        
                        
Continuous     Alkaline         Lithium         Lithium 
Current        Duration         Duration        Performance
Drain          to 0.90 V        to 0.90 V       Advantage
(mA)           (hours)          (hours)         (factor)
                        
0.3             8700            8700            1.00
30              72.00           83.00           1.15
100             19.50           25.00           1.28
125             12.00           17.50           1.46
250             5.90            8.75            1.48
300             4.50            8.20            1.82
500             2.25            4.83            2.15
750             1.00            3.17            3.17
1000            0.40            2.00            5.00
1100            0.30            1.66            5.53
1250            0.23            1.58            7.04
1500            0.08            0.90            11.25

If the specifications for a device give Watts instead of mA,  use:  
   Watts * 1000 / Volts = mA
where Volts is the sum for all batteries in series.
For example, 0.75 Watts @ 6 Volts (four AA's) is equivalent to 125 mA.

Surprise!  The performance of Lithium AA's increases relative to Alkaline
AA's as the current requirements of the device increases!  For example,
Lithiums can last more than 9 timeslonger than Alkalines in high drain
devices pulling 1400 mA, but not quite twice as long in devices drawing
only 400 mA.

If longevity is your only criteria for choosing between Alkaline AA's and
Lithium AA's, Lithium AA's are the obvious choice for all applications
with current requirements at or above about 25 mA.

If cost is to be fully considered however, you should divide your cost for
Lithium AA's by your cost for an equal number of high quality Alkaline
AA's to determine your cost ratio.   Then, knowing the load of your
device, use the above table to find the performance ratio had at that
number of milliamps.  If the performance ratio exceeds your calculated
cost ratio, buy Lithiums instead of Alkalines.

Lithiums offer other advantages that might deserve consideration:  A
weight of 15 grams vs. Alkaline's 23 grams, a shelf life of 10 years vs. 5
years, a higher initial voltage of 1.8 volts vs. 1.6 volts, and superior
performance at low temperatures.

This document (the spreadsheet) was not produced by Eveready Battery
Company, Inc. It is an original creation.  It correlates independent
performance data which was extrapolated from curves plotted in datasheets
provided by Eveready Battery Co., Inc.   I requested these data sheets
from Eveready Customer Service in January, 1998, so I consider the data to
be current, but there is some inaccuracy inherent to my having obtained
the numeric values by extrapolating the x-y coordinates associated with
points on a curve.  In other words, I can not guarantee the accuracy of
this data.

Datasheets:     Energizer L91 datasheet, Form No. BE 381
                Energizer E91 datasheet, Form No. EPS



-- 
/---------------------\
   Michael K. Davis              
  zilch0@primenet.com                   
  MIME Attachments OK
\---------------------/

FROM: davem@cs.ubc.ca (Dave Martindale)
SUBJECT: Re: Charging NiMH batteries
DATE: 1 Jun 1998 06:28:31 -0700
ORGANIZATION: Computer Science, University of B.C., Vancouver, B.C., Canada
NEWSGROUPS: rec.photo.digital

"Gregory Thomson"  writes:
>Then, i just bought the "5 hour" radio shack charger.(23-406)..though
>cheaper, only puts out 300 milliamps for charging.  Based on what you say, i
>should exchange it for the 23-405  "one hour charger" which costs $30 as
>opposed to $15, since it (presumably) puts out much higher charge rate, will
>extend batt life, and would be easier since 1 hour is a fast charge rate.

The 1 hour charger is better *if* it detects full charge and shuts itself
off when that happens.  If it always charges for an hour regardless of
battery state, it's much worse than the 5 hour charger.

>Final question.....how long is shelf charge life of a fully charged nmh?
>After a week, should one give em an hour on the one hour charger?  Will that
>hurt it if its already charged full?

NiMH apparently lose 10% of their charge in the first day, and about 2%
per day after that.  Loss after a week can be significant.  If you really
want full capacity, charge just before using.  If you have a good charger,
the "topping off" charge will only take a few minutes and won't hurt
the batteries.

	Dave

From:             "Willem-Jan Markerink" 
To:               eos@avocado.pc.Helsinki.fi
Date sent:        Mon, 7 Feb 2000 21:44:27 +0100
Subject:          Re: EOS: Need help with PB-E1!
Priority:         normal
Send reply to:    eos@avocado.pc.Helsinki.fi

On  3 Feb 00 at 20:44, YEGEY@aol.com wrote:

> Hi All,
> For everyone who uses PB-E1 on their EOS1/1N/3  with NiCad E1 batteries :
> Could you tell me if these batteries accumulate a "memory " effect - so it
> hold less and less charge and if so - how to deal with it? Or is there any way
> to deal with it besides buying a new one?

I recommend you first read a few chapters on my homepage about this 
so called 'memory' effect:

http://www.a1.nl/phomepag/markerink/mainpage.htm

It's quite a bit different than most manufacturers want you to 
believe....nothing less than a very persisting urban myth, all based 
on some very controlled & repetitive NASA experiments.

Btw, did anyone notice the interesting EOS-1V table of battery-type 
vs number of films, at +20C and -20C?
It clearly shows that NiCd still has an advantage over NiMH at such 
extreme temperatures, despite being less than half the nominal 
capacity in mAh....

 (Number of 36-rolls until complete empty/shut-off, last 2 collumns added by WJ)

                         Remaining   Nominal capacity
             +20C  -20C   capacity     (estimate/market-average)
-----------------------------------------------------------------
2CR5          50    12      24%         1300mAh

8x Alkaline   85     5       6%         2000mAh
8x Lithium   120    50      42%         3000mAh
8x NiCd       35    24      69%          500/600mAh
8x NiMH       70    20      29%         1000/1200mAh

I knew NiCd was better than NiMH in cold in a relative context, 
but this even proves it is better in an *absolute* context too....

Also note that the above Canon table is based on NiCd's from 5-600mAh, 
while currently cells exist that are twice this capacity (1100-1200mAh). 
This puts them on the same level as Lithium under those arctic 
conditions.

--                 
Bye,

Willem-Jan Markerink

      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


[note: 'a-one' & 'en-el'!]

If you have any question, remark, comment, want to share some philosophy or just want to express your opinion about these pages, feel free to send email to: w.j.markerink @ a1.nl