NiMH in Cordless Phones...confused

[PeAK]

The newer Panasonic cordless phones now use replaceable AAA NiMh batteries. The strange thing is that they also warn against using NiCd batteries which I thought were more robust than NiMh (using trickle charging) and also more durable when run down to very low voltage. The other thing is that I thought NiCads could be used in any charger designed for NiMH ? I'm confused about the role of an NiMh battery in a cordless phone...true progress or a step backward due to the large scale availability and price advantage of NiMh ?

PeAK

 

[Turbo Guy]

I agree with your thoughts and the only logical reasons for advising against useing Nicads would be not good for the enviorment and most are lower capacity so the charge rate would be a higher C rate.


A AAA NiMH could be 900 mAh and a AAA Nicad might be only 400 mAh. With a built in deicated charger there would be a large difference in charge rates.

Nicads are to become a thing of the past.

 

[Wattnot]

Nicads will never be a thing of the past. No battery technology is perfect and each has it's advantages. I still have 20 year old nicads that still hold a respectable charge.

However, I like nihms for the cordless phones. My ATT cordless set came with nicads which were toast after 6 months. I replaced them with some nimhs years ago and they're still working fine.

The problem with the nicads in cordless phones is the intermittent use (memory issues) and overcharging. Nicads work best when they're charged all the way, and discharged all the way. That rarely happens with the way most people use cordless phones.

 

[Turbo Guy]

Nicads will become a thing of the past due to goverment regulations. They contain heavy metails which is damaging to the enviorment. They are already banned in some countries just like electronic solder which contains lead.

Nicad batteries do not develop memory, they can develop voltage depression but would have no effect on them in most uses such as cordless phones ,TV remotes etc. as voltage depression is only a problem at higher discharge rates. NiMHs also develop voltage depression, just like Nicads. many do not know the difference between memory ( a myth) and voltage depression which is real. Voltage depression in Nicads or NiNH is corrected by discharging to 0.9 volts per cell and charging which is also known as cycling.

I have 20 plus year old Nicads which are still good. I have 12 year old NiMH which are still good.

I have 3 year old Nicads and NiMH which are no good. Not all cells / batteries are created equal.

I have been using Nicad batteries since 1963 and NiMH since approx. 1987.

Nicads can tolerate overcharging a lot better than NiMH. In fact Nicads can be trickle charged at 1/40 24/7 without issue and can be charged at 1/10C for days without issue.

 

[Backpacker Light]

The problem with the nicads in cordless phones is the intermittent use (memory issues) and overcharging. Nicads work best when they're charged all the way, and discharged all the way. That rarely happens with the way most people use cordless phones.

This is an interesting thread.

Cordless phones are a great thing -- until the batteries die and you look at the cost to replace them. You can almost buy a new phone for the same price as what the battery pack costs. With the now common two-three or even four handsets, you are looking at a major investment if you need to replace all of the battery packs at the same time.

To hopefully extend the life of the battery pack, our family now intentionally leaves the phone out of the charger until dead. Then we fully charge it, and then leave it just laying around again until dead.

Will this actually help extend the life of the battery pack? My fear is what I have read about the possible damage done to Nicad's if over-discharged. There is no battery indicator on the phone though.

I am glad to read some phone's now accept the regular individual cells, instead of only those specialized battery packs.

 

[Turbo Guy]

Without knowing how the chargers in the cordless phoes really work it is hard to say to what extent the batteries are damaged by constant charging. I have a cordless 2.4 Ghz Uniden that is 5 years old and the original abttery is still good. It stays in the cradle 24/7for months at the time. About every three months I leave it out for a day or so then back it goes. I had another one that was used a lot more and the batery lasted just over a year.

The general consenious is to not leave NiMH on a slow (trickle) charger and in fact not to even use one for charging them. I have a set of two years old RAYOVAC hybrids which were only charged with a 110 mAh charger.These were a set of 8 in series used in one of my R/C transmitters and on average were charged every 10 days. They were placed on charge when they read 9.4-9.6 volts under load(approx. 130 mA) and where charged to 11.5 volts. I recently replaced them with a set of Eneloops 08-0815 Date code?. I cycled the Eneloops and the Hybrids. I discharged them in sets of 8 and then recharged and discharged one of each chosen at random. Both discharge test the hybrids matched the Enelops under a 1amp. load and in fact delived 60 to 80 mAh more capacity.

 

[PeAK]

.
.
.
To hopefully extend the life of the battery pack, our family now intentionally leaves the phone out of the charger until dead. Then we fully charge it, and then leave it just laying around again until dead.

Will this actually help extend the life of the battery pack? My fear is what I have read about the possible damage done to Nicad's if over-discharged. There is no battery indicator on the phone though.

I am glad to read some phone's now accept the regular individual cells, instead of only those specialized battery packs.

I've found that when my phone fails to recharge, it is because one of batteries (in the pack of three) fails to take charge. When you run down a phone pack, it is possible that the cell with the lowest capacity might suffer from voltage reversal if the phone can operate at low voltages for extended amounts of time. What I found to bring back the pack is to attach individual leads to the independent channel charger from the weak battery (need to remove plastic shrink wrap)...so far so good.

PeAK

 

[Mr Happy]

I had the same good experience with a Uniden phone (a 5.8 GHz one in my case).

The original NiMH battery packs in both handsets lasted 5 years before the capacity was reduced to about half the original level. The handsets are left in the charging cradle 24/7/365 when not actually being used.

I bought generic replacement batteries for about $10 each, which is about the same cost as 4 loose AAA cells. The replacement batteries are working fine and give a nice long run time again.

 

[SilverFox]

Hello PeAK,

My Panasonic phone uses 4/3 AA cells. The instructions mention keeping the handset on the charger when not in use. I believe they have a little bit of smarts incorporated into the charger and it shuts off instead of constant trickle charging.

Time will tell if this is the case or not.

My old phone was a Sony and I alternated two NiCd battery packs with it. Twice a year I would do a full discharge followed by a 16 hour 0.1C charge. One of the original battery packs was still working, and the other I had to replace, but the phone was in constant use for a little over 10 years.

I ran a set of baseline tests on the batteries in the Panasonic phone and will have to see how well they do.

Regarding NiCd cells, the latest information is that Sanyo is no longer providing this chemistry. They stopped manufacturing them last year, and have also stopped distributing them. What is left is old stock and when that is gone that will be the end of Sanyo NiCd cells.

I expect other manufacturers to follow suit.

Tom

 

[dannstrait]

I can't add much more than Mr. Silverfox/Turbo Guy have already, but just last week I was thinking the same thing as the OP about my Panasonic phone. It uses two Panasonic 630 mah NiMH AAA batteries. I've had the phone for about 8 months and figured I'd put my C9000 to work and run a refresh/analyze cycle after a discharge @ 100mah. Upon removing the batteries from the phone, I saw Panasonic's recommendation not to use NiCads and had to scratch my head. I believe Panasonic is advising to avoid NiCd batteries for 3 reasons:

1) Potential charge rate concerns (trickle charge rate may be based on 630mah capacity)
2) Environmental concerns
3) Sales!! Panasonic doesn't sell NiCd's (right?). On the back of the phone they say to use only Panasonic-brand NiMH batteries. I'm positive any manufacturer's AAA NiMHs with a comparable capacity would work in this phone. Whenever possible, Panasonic naturally wants people to purchase Panasonic products - batteries included.

No real complaints here though. The ability to accept loose AAA cells was a major reason why I bought the phone in the first place. Good design move on behalf of Panasonic! I was tired of paying $20 for new battery packs when new phones cost $25. Additionally, I knew I could individually condition the cells by throwing them into the C9000.

As Silverfox suspects, I too believe this phone has some smarts in regards to charging. After cycling my batteries and putting them back in the phone fully charged, the phone displayed the "Charge for 7 hrs" message while flashing the battery indicator (indicator showed 1 of 3 bars remaining). This message is displayed anytime the batteries are removed and reinserted regardless of state of charge. Knowing the batteries were fully charged, I put the phone in the base for a minute, removed it, and go figure - the battery indicator changed to 3 of 3 bars.

The phone must have some type of circuitry to detect a full battery and perhaps it then goes into a trickle mode. 7 hrs x 90mah = 630mah. Obviously, 90mah would be way too high for a trickle charge current so I think/hope the phone has some type of peak detection/trickle charge scheme.

Silverfox has pointed out that trickle charging NiMHs for any extended period of time can be damaging in many cases. Erring on the side of caution, I try not to leave the handset in the cradle 24/7/365. I use the phone for about 1 hour a day. I put the phone in the cradle every other day or so and always have plenty of runtime. Their refresh&analyze capacity = 550mah so they're still pretty much up to spec. Since these cells are so easily and economically replaced, I wouldn't be worried even if I did leave the phone cradled 24/7/365.

 

[yellow]

cordless phone is THE typical example of a gadget to build up cell memory with Ni-Cds.
Possibly the only application that really had battery memory damages in real life and on large scale:
never totally discharged, typically always in charger/cradle

Ni-Mh should be much better here + offer more power inside, no need to dislike them

 

[monkeyboy]

I'd be interested to know if anyone has done any testing on eneloops / hybrids to see how well they hold up under constant trickle charge compared with regular NiMh. I'm thinking about replacing some dying phone batteries (AAA) with eneloops.

I know they've only been around for a couple of years but that should still be enough time to produce some valuable data.

 

[dannstrait]

I'd be interested to know if anyone has done any testing on eneloops / hybrids to see how well they hold up under constant trickle charge compared with regular NiMh. I'm thinking about replacing some dying phone batteries (AAA) with eneloops.

I know they've only been around for a couple of years but that should still be enough time to produce some valuable data.

Please see Silverfox's thread that I was referring to before:

http://www.candlepowerforums.com/vb/showthread.php?t=224393

 

[monkeyboy]

Thanks dannstrait, I must have missed that one.
I think I'll look for different NiMh cells.

 

[GarageBoy]

Doesn't NiCd only develop memory if u charge and discharge to the same point?

 

[VidPro]

Doesn't NiCd only develop memory if u charge and discharge to the same point?

that was how it was "discovered" ooooh , that the battery had "memory effects" wow a battery with a mind , imagine that.

but basically they just had a repeating occurance of an exacting charge discharge level, and it showed up on a graph really well. at the last point the chemicals had not been cycled, the chemicals not cycled were less vibrant. the same thing had been happening here on earth for thousands of years, before the astronaughts discovered it.
the same basic thing occurs in the other rechargables to various levels depending on the chemistry , whatever it wants to be called by experts, the chemicals that fell into enthropy and chaos, remain in enthropy and chaos till the forces of great power realigned them
its not exactally the achillees heel, but it does explain why Atlas has back problems.

what i am saying its just the practical occurances of most of the things in nature, to defy them is to believe that man has conquered nature , will not be decomposing in 100 years, and will make a battery that never requires conditioning or power , but then the decay rate of the isotope UU576 will not have a memory, anyone will remember.

:thinking: wtf

 

[PeAK]

Doesn't NiCd only develop memory if u charge and discharge to the same point?

Under real world conditions this can happen with batteries that are disconnected from the electronics at some fixed voltage (voltage cutoff circuits). Even then, the correlation between voltage and capacity has a lot of noise. Cell reversal and uneven cell capacity in a string of cells is more often the problem.

Reference: Google search on terms "Nicad memory satellite"

PeAK

 

[Turbo Guy]

Even then, the correlation between voltage and capacity has a lot of noise. Cell reversal and uneven cell capacity in a string of cells is more often the problem.

True.

What is commonly called memory is really voltage depression. It is not that the cells will not discharge to a lower voltage under load it is that they will be able to maintain as high an average voltage or maintain useable voltage under a heavy load when they reach the point they have been cycled down to. In very low drain devices this is really not an issue.

Many consumer devices have circuits which are really designed for non rechargeables even if the are supplied with rechargeable. A typical aklaine cell is approx. 1.6 volts when fresh. A typical Ni cell is 1.45 soon after being charged and will settle to 1.35 to 1.4 in a day or so even if it is a LSD one. This means with a freshly charged Ni you have 0.15 volts per cell less at best. Due to the simple fact that many consumer devices will stop working or atleast give a low battery indication at close to 1.1 volts per cell total ,cell reversal is not normal with devices with 2-4 cells in series unless the cells are of very low quality or very used / abused.

 

[Backpacker Light]

I've found that when my phone fails to recharge, it is because one of batteries (in the pack of three) fails to take charge. When you run down a phone pack, it is possible that the cell with the lowest capacity might suffer from voltage reversal if the phone can operate at low voltages for extended amounts of time. What I found to bring back the pack is to attach individual leads to the independent channel charger from the weak battery (need to remove plastic shrink wrap)...so far so good.

PeAK

Not entirely sure what you mean by this, PeAK. I still have my old "dead" cordless phone, and thought maybe I would try this to revive the battery pack.

I do have a independent charger, a Sanyo MQNO5U. But how do you run a lead to it? Do you make a pair of short leads with alligator clips on the two ends?

To connect to the charger, an alligator clip might work on the negative bottom contact, but the top contact has nothing to attach and hold to. Just tape the bare wire (without a clip at all) to the flat contact?

And the battery pack, do you remove the plastic AND take apart the batteries? If you don't, how do you test for the one bad cell, and then charge it, if it is still in series? You can't do that right? And if I take the batteries apart, I wouldn't need the leads, and could just throw the bad cell in the charger directly.

I haven't taken the plastic off the cells yet, maybe I should start there and see what I'm dealing with.

Hope this doesn't sound like stupid questions, but I have never tried this before.

 

[Mr Happy]

Not entirely sure what you mean by this, PeAK. I still have my old "dead" cordless phone, and thought maybe I would try this to revive the battery pack.

I do have a independent charger, a Sanyo MQNO5U. But how do you run a lead to it? Do you make a pair of short leads with alligator clips on the two ends?

To connect to the charger, an alligator clip might work on the negative bottom contact, but the top contact has nothing to attach and hold to. Just tape the bare wire (without a clip at all) to the flat contact?

And the battery pack, do you remove the plastic AND take apart the batteries? If you don't, how do you test for the one bad cell, and then charge it, if it is still in series? You can't do that right? And if I take the batteries apart, I wouldn't need the leads, and could just throw the bad cell in the charger directly.

I haven't taken the plastic off the cells yet, maybe I should start there and see what I'm dealing with.

Hope this doesn't sound like stupid questions, but I have never tried this before.

This is probably something you would do more out of curiosity than out of practical value.

You have to take the shrink wrap off the pack at least to the point where you can reach the bare metal terminals of each cell. Then you can attach alligator clips or use a charging clamp to access individual cells in the pack. The cells will be welded together with metal strips that the alligator clip can hold onto.

An ordinary charger won't help much for the reconditioning though. You need something like an MH-C9000.

Also the cells in an expired pack I removed from my cordless phone were of a non-standard size. An AAA cell is about 44 mm long, but these cells were 50 mm long with flat tops.

The best way to revive a dead pack is to replace the pack or replace the cells with fresh ones and reassemble using the old connector and new shrink wrap or electrical tape. Although without a battery welder you would have to solder to the cells, and this needs extra care to avoid damaging them with the heat.