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NiMH Batteries

05/07/2008 9:03 PM

I have a set of wireless phones handset powered by AAA 1.2 volt Nickel Metal Hydride batteries. After 2/3 years of faithfull service the phones started behaving erratically. I diagnose that the batteries were probably dying, and so replaced them with a "leading" brand of consumer batteries of the same size and type. This was despite dire warnings from the manufacturer of the phones that I should "only use Brand X (their own!) batteries". As you can guess, these did not work very well so, I tried another well know brand (the original batteries were very hard to find). The second lot worked no better. Discretion being the better part of valour, I gave up and trekked to an outlying suburb and found the original batteries and they work really well. My question is this: why do some batteries work so much better even though they are supposedly the same spec? The others were household brand names, no cheap and nasty ones. In fat they are all about he same price. It is obviously in a manufacturer's interest to lock consumers into their own brand of batteries but how do they do that? As an Electronics Engineer by training, I can only assume that it has something to do with charging rates, lots of intermittent use etc etc. Has anyone got any ideas as to how they achieved this? My next stop is the multimeter and an analysis of voltage levels, charging rates etc :-( Maybe someone can save me all that hassle..... Many thanks in advance.

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#1

Re: NiMH Batteries

05/07/2008 9:25 PM

What exactly was the problem? Was it replacement batteries not charging properly (does the charging circuit really rely on the characteristics of the battery in order to regulate charge properly)? or perhaps the replacement battery's impedance is too high causing the output voltage to sag too much when the phone drew large amounts of current (causing erratic operation).

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#2

Re: NiMH Batteries

05/07/2008 9:55 PM

Hello sensys001

I have found this problem occurs amongst NiCd, NiMH and the later Li-ion type of batteries.

There appears to be no pattern, and sometimes a win is achieved, when a different make is both cheaper and better.

One conclusion I have reached, is that sometimes re-chargeable batteries sit for long periods on an importer's, warehouse, or shop shelf, and the cells discharge, then age while discharged.

This means, as you have discovered, that the "new battery" you purchased from the shop, may be several years in a discharged condition, waiting for an unwary buyer to purchase and try to use.

The supplier from which you purchased the new battery, may not know the battery is really quite old.

There are "Smart Chargers" which actually can "revive" such batteries, and they work by firing a succession of short but high current pulses of DC through the battery, and in that way the battery becomes "revived", after a full charge/discharge cycle with this type of charger has been used three or four times.

Details of a commercially made charger of this type for NiMH batteries are here: http://www.thomas-distributing.com/maha-powerex-mh-c204w-nimh-battery-charger.htm

I use a "Smart" charger 6/12/24Volts @ 10 Amps capacity, for lead-acid batteries, which also has a micro-processor controlled output.

"Smart" Battery chargers which are "intelligent", and have an algorithm for the charging, which obtains the very best out of a connected battery, are now made for various types of re-chargeable batteries.

These "new technology (intelligent)" chargers are replacing many chargers, once you try one, you never go back to the older "El cheapo/brute force" charger.

Kind Regards....

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#3

Re: NiMH Batteries

05/08/2008 11:33 AM

It may seem obvious, but I have to ask, were you using Ni-MH batteries when you said "and so replaced them with a "leading" brand of consumer batteries of the same size and type." If you did replace them Ni-MH, and they were around the same mAh rating, I don't know of any way the phone would know the difference. If the "leading brand" had a much higher mAh rating, I suppose the charger might not charge correctly (lower ESR on the battery?), but I don't think that's likely, it should just take longer to reach full charge.

Did you let the phone charge overnight after replacement? I've got a few cordless phones that use standard Ni-MH, and I've replaced batteries with no trouble, not sure what's going on.

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#4
In reply to #3

Re: NiMH Batteries

05/09/2008 6:06 AM

Guys, I did replace them with Energizer Ni-MH batteries of the same rating (800 mAH). Also tried VARTA of same nominal spec. I agree that "the phone shouldn't know the difference" hence my puzzlement. When I find some time, I'll grab a multimeter and do some tests. Do hold your breaths, guys! Thanks for the input anyhow.

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#5

Re: NiMH Batteries

05/09/2008 9:18 AM

One thing I would look at (not being into electronics except as a hobby) is whether there is a discernable difference in the fit of the batteries, one mfgr to another, in the phone? In other words, do the terminals contact the points fully with the off-brand units?

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#6
In reply to #5

Re: NiMH Batteries

05/09/2008 9:44 AM

Good point. I once used cheap knockoffs which expanded during the recharging process. Switched to Maha Powerex and Energizer and have had no problem since.

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#7

Re: NiMH Batteries

05/09/2008 9:48 AM

Excellent question. I had a similar problem with a camera that used two rechargeable AA batteries with a nominal output of 1.35 Volts. I'm not sure what type that makes it, but two non-rechargeable AA batteries at 1.5 Volts drove the digital camera crazy. It simply would not work normally, so I was unable to use it until I recharged the batteries that came with the camera.

Most families of digital circuits can tolerate a little variation of supply voltage without stepping out of spec. and continue working fine. Rechargeable batteries maintain a nominal output right up to the point in which they are exhausted. Other batteries drop of steadily as they are depleted. This fact alone would make it preferable to use rechargeable batteries because the output would be maintained nicely right up to the time that it was necessary to recharge them.

Most families of digital devices operate at 3V±0.3V or 5V±0.5V unless you go with CMOS which can generally operate between 5 and 15 volts. But one thing that might explain your problem and mine would be a case where the designer used 5 volt logic powered from two rechargeable batteries and a DC to DC converter to boost the voltage up to 5 volts. Then, if you used two 1.5 volt batteries, your output from the DC to DC converter would be too high (6++ Volts) for reliable operation. Or the DC to DC device might overheat and shut down and recover rapidly causing erratic behaviour.

In any case, I'll be watching for other explanations as I too am curious as to possible causes. But without opening up my camera and performing some reverse engineering, that would be my guess. If you liked this answer, please rate it. I'm new to the board and would like to have more positive ratings.

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#10
In reply to #7

Re: NiMH Batteries

05/09/2008 1:50 PM

Wouldn't we all!!

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#12
In reply to #10

Re: NiMH Batteries

05/09/2008 3:08 PM

Yes, and despite the fact that yours IS a VERY Good Answer, somehow, I just can't bring myself to vote for it...

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#15
In reply to #12

Re: NiMH Batteries

05/09/2008 5:29 PM

Spoil sport!!

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#8

Re: NiMH Batteries

05/09/2008 10:22 AM

I've had a similar problem--also with a portable phone. Tried a reputable brand NiMH battery Vs the recommendation and it didn't work. I will follow this thread.

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#9

Re: NiMH Batteries

05/09/2008 10:40 AM

Hi sensys001,

I would have thought the Energisers would have worked well. I have been unhappy with Chicago Electric batteries bought from Harbor Freight Tools (a China importer?).

If I try to use them in my digital camera, I am lucky to get 2 pictures before the camera says they are low and won't operate. I have tried the Nicad and the NiMH varieties, and I have a charger designed for the latter. The lower voltage may be part of the problem.

My wife bought me a radio for the shower. I takes 3 of the AAAs. I put in 1 recharged NiMH with 2 Duracell Alkalines that were already low on voltage. After about a week it got distorted so I checked the batteries. The Duracells were the same voltage as before, but the NiMH was 0 volts! It claims to have 700mAh rating. I am trying the same experiment again with another one now. I expect similar results.

S

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#11
In reply to #9

Re: NiMH Batteries

05/09/2008 1:57 PM

That is a bad idea always to mix batteries of different types, manufacturers and age.

All the cells in a unit (camera, radio or whatever) should be fully identical (bought together from the same batch on the same day) and NEVER let them get to the point of any battery getting reversed polarized, which is what happens when you do what you did.....

Reverse polarization kills most rechargeable batteries.

It is not quite so bad when done with primary cells as they will get thrown away anyway, but secondary cells need careful usage.

You also need a charger that charges each cell individually and not 2 or more together....one that does not overcharge, one that tops up only, for nicads, one that discharges first to about 1.1volt

Car batteries, which cannot be easily charged a cell at a time, usually fail in only one cell and the whole battery must be junked.....

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#14
In reply to #11

Re: NiMH Batteries

05/09/2008 5:29 PM

"Reverse polarization kills most rechargeable batteries."

But if this happens in a week of only listening while I am showering, do I care? It doesn't seem to be much good anyway.

"It is not quite so bad when done with primary cells as they will get thrown away anyway, but secondary cells need careful usage."

You must have a different definition of primary cells than I do. What's your definition?

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#16
In reply to #14

Re: NiMH Batteries

05/10/2008 4:51 AM

You wrote:-

You must have a different definition of primary cells than I do. What's your definition?

I do not have a definition of my own, I follow the standard rules as it saves us all from any misunderstandings....

A Primary cell is not rechargeable, a secondary cell is rechargeable.

Please read the following links, as this is the correct terminology to use when talking about batteries. It is also standard school physics information that also gets repeated in the first year at University, many times.....I did not invent this terminology! I just use it:-

Primary cell

Secondary cell

I forgot to mention before that if a 12 volt lead acid battery, is discharged too far, the first cell that is completely discharged (each cell has different characteristics, but generally an end cell that has had slightly more frost in winter, or got too hot in summer or both!!), will get reversed polarized if the battery is further used. The whole battery is now just junk!!! Car batteries get heavily damaged from just one time, in one cell polarization reversal....and that cell can just chemically collapse, from one minute to the next.....

I personally have a rule for all 12 volt Pb batteries for a minimum of 12.6 volts, maximum 13.4 volts for charge/discharge, even for deep cycle batteries as all Pb batteries last far far longer when following this as far as possible.....in most cars, the charging goes as high as 14.4-6 volts and we accept the short lifetime as being normal....

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#17
In reply to #16

Re: NiMH Batteries

05/10/2008 5:40 PM

OK, don't get defensive. This is what I would have called a primary cell:

http://en.wikipedia.org/wiki/Weston_cell

but I don't think anybody uses them anymore. Thanks for the update.

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#18
In reply to #17

Re: NiMH Batteries

05/10/2008 7:45 PM

That is a primary cell, its mentioned further down in the article....

But that primary cell is used as a calibration voltage, not as a supplier of power....in fact, if you take power from it, its not good at all.....the article is really excellent and mentions that point.

That is a very specialised cell type that even skilled engineers only learn about in the classroom, few will ever touch or see one even!!

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#19
In reply to #18

Re: NiMH Batteries

05/11/2008 6:24 PM

Hi Andy!

The kind of cell StandardsGuy referred to is what came to my mind when I saw the term "primary cell", but you are right: I haven't seen one since I left College...

I hadn't heard the term used for non-rechargeable power cells. Thanks for the education!

Dick

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#20
In reply to #19

Re: NiMH Batteries

05/12/2008 9:15 AM

No problem, we all learn new things on CR4, which is why I like it so much!!!

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#21
In reply to #18

Re: NiMH Batteries

05/12/2008 8:08 PM

"But that primary cell is used as a calibration voltage"

Yes, I know. We had some in the lab where I work, but I think it's been about 20 years. Now we use zener references and a Josephson Junction array.

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#22
In reply to #17

Re: NiMH Batteries

05/13/2008 12:44 AM

Hello StandardsGuy

I last used a Weston Reference cell, back in 1963.

As you say, they have become obsolete, and there are electronic reference standards which are commonly used, and are also cheaper and more convenient.

Most people nowadays would not know what a Weston Cell was.

Kind Regards....

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#13

Re: NiMH Batteries

05/09/2008 4:09 PM

Most Ni-Cd and Ni-MH are 1.20V. Some are 1.25V. I also find problem with them not holding charge long enough. Its a hit and miss. My 2100mAh Duracell works great but their 2500mAh lose charge in a few days. Try charge them up with a overnight charger before you put them in the phone.

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