Why do they recommend constantly charging electric toothbrush, cordless phone etc?

[NeoPTLD]

Many cordless phone and electric toothbrushes uses NiCd to these days. My Sonicare instruction recommends putting it on charger after each use.

I don't find any reference about modern NiCd batteries being immune from memory effect and I think its unavoidable with NiCd technology.

Why do they still recommend you to charge it after each use?

 

[L00PY]

I suspect it's because they just don't monitor the voltage very closely. If the end user never sees the inevitable slight voltage depression that comes with constant trickle charging, they'll never blame the "memory effect". Given that you're not moving the battery into another device, it should be easy enough to design for it.

Bottom line: Since NiCd Batteries do NOT have "memory", just put it on its charger after each use.

 

[Amaroque]

Originally posted by: NeoPTLD
Many cordless phone and electric toothbrushes uses NiCd to these days. My Sonicare instruction recommends putting it on charger after each use.

I don't find any reference about modern NiCd batteries being immune from memory effect and I think its unavoidable with NiCd technology.

Why do they still recommend you to charge it after each use?

If you constantly keep it charged, it will wear down faster. Therefore you'd have to buy a new one sooner. Sounds like great marketing to me.

There is a very similar recent thread here.

 

[pm]

Although this is actually a suprisingly controversial issue, most agree that the "memory effect" was an early problem in the chemistries of NiCd where if the battery is discharged to the exact same discharge state repeatedly which caused dendritic crystalline growth on the anode leading the battery appearing to be discharged when there was still capacity remaining. This problem was isolated to only sintered plate NiCd batteries. Newer NiCd batteries types are capable of >600,000 cycles at <2% depth of discharge[1].

What most people term the "memory effect" now actually comes from having overcharged the battery repeatedly leading to a temporary voltage depression. Detecting overcharge is actually a fairly difficult task which recent research has helped with a lot. The earlier problems (before 1995-ish) with overcharging, and with memory effect have been largely eliminated in most applications with newer methods of detecting full-charge using a combination of temperature gradient sensing and voltage droop detection.

In the absence of high discharge rates (>15 times the capacity of the cell), overcharging and high-temperature operation (>50C) NiCd batteries have extremely long life and have been used continuously in industrial applications and safety equipment for over 15 years.

As noted in "The Characterization of Nickel-Cadmium Batteries for Telecommunications Applications, Part 2" by Anthony Green, INTELEC 97:
"In terms of long term reliability of nickel cadmium batteries, it is possible to give many examples. He in Australia, the Sydney Opera House were so satisfied by the 15 years service obtained from their original nickel cadmium batteries that they replaced them in 1992 with the same technology" and later "The Eurostar and Le Shuttle trains passing through the Channel Tunnel use exclusively nickel cadmium batteries in steel containers. These have been in service since 1994 and are based on French Railway's 20 years experience with the product."

[1] "Development of High Power Nickel-Cadmium Batteries for Hybrid Vehicles", Disosway, M.;
Battery Conference on Applications and Advances, 1998.

 

[SaintTigurius]

nicely done dexter,

 

[FrankSchwab]

Just a quick $0.02 -
Most of the "popular" opinion on memory effect is probably due far more to overcharge and overdischarge of cells than anything having to do with memory. From what I've heard, basically anytime a NiCd shows a reduced life, people call it "memory effect". Far more likely is just chemical damage.

If you overcharge a NiCd (charge continuously above around c/30), irreversible damage can be done to the cells as a result of heat and the chemistry that is occurring. Cheap chargers that don't monitor temperature do this often; the problem is even worse with NiMH.

If you overdischarge a pack of NiCd cells, irreversible damage also occurs. In any pack (except extremely well-matched ones), statistically one of the cells will have a lower capacity than the others. If you run the pack down until that cell is completely discharged, but the other cells still have some oomph left, they will essentially be reverse-charging the cell, causing "bad things" to happen internally. That cell gets damaged, and fully discharges even sooner the next time you run the pack down; soon, it dies completely. Think about that the next time you decide to drive "just one more screw" with your battery-powered drill that's barely turning the chuck.

/frank

 

[Jeff7]

Originally posted by: NeoPTLD
Many cordless phone and electric toothbrushes uses NiCd to these days. My Sonicare instruction recommends putting it on charger after each use.

I don't find any reference about modern NiCd batteries being immune from memory effect and I think its unavoidable with NiCd technology.

Why do they still recommend you to charge it after each use?

Cordless....maybe some of the 900Mhz/2.4GHz things do; cellphones use Li-ion, at least mine does. I imagine that a lot of companies might use Nicad either to get rid of old inventory, or else because it's cheaper. NiMH should be replacing NiCad; that's what I've done at home. Much better lifetime, and they can charge faster. Heck, I even ripped apart my ailing Dustbuster and replaced its NiCad batteries with NiMH's, and it runs much longer than it did when it was new.

This "memory effect" is sounding more like a renamed version of either "overcharging" or "deep discharge."

 

[pm]

There are advantages to NiCd's over NiMH batteries. Extremely high discharge rates are one; with a NiCd, you can discharge at 30C or more (30 amps from a 1000mAh AA pack - pretty amazing actually), but try and get much above 15C with a NiMH and watch the voltage droop big time). So high-powered cordless equipment (like high-end cordless screwdrivers) are usually NiCd still. Also NiCd's work a bit better than NiMH's in cold temperatures (0 celcius). There are also safety concerns to charging NiMH's in cold conditions (they vent hydrogen.. or used to anyway). Lastly, it's easier to build a NiCd charger than an NiMH one - although in these days of single IC droop peak chargers, this isn't the issue that it once was.

But for household applications, NiMH's are more environmentally friendly and have better energy per weight ratios. Most things are headed NiMH or Li-poly.

 

[0roo0roo]

yup...rc cars and stuff are good with nicd. nihm is best for moderate drain stuff like cameras.

 

[mooncancook]

yup...rc cars and stuff are good with nicd.

In the world of RC cars, NiMH has replaced NiCd for a while now. Right now ppl are running NiMH 3300 MAh cells. NiCd has memory problem, lower capacity, more hazardous to the environment, and performance wise NiMH are catching up, that's why the RC world abandoned NiCd.

I was very suprised that the Sonicare toothbrush costing over $100 use cheap NiCd battery. And the new home phones still use NiCd. Many of the phone i used had the NiCd battery died. The NiCd in my current Panasonic phone died, and i didn't bother to buy the expensive replacement. I revitalize it with standard NiMH cells with a litter soldering work, and it's been working great with longer talk time

 

[FrustratedUser]

Originally posted by: NeoPTLD
Many cordless phone and electric toothbrushes uses NiCd to these days. My Sonicare instruction recommends putting it on charger after each use.

I don't find any reference about modern NiCd batteries being immune from memory effect and I think its unavoidable with NiCd technology.

Why do they still recommend you to charge it after each use?

Because most of them use NiMH batteries and they don't suffer from the 'memory effect'.

 

[FrustratedUser]

Originally posted by: mooncancook

yup...rc cars and stuff are good with nicd.

In the world of RC cars, NiMH has replaced NiCd for a while now. Right now ppl are running NiMH 3300 MAh cells. NiCd has memory problem, lower capacity, more hazardous to the environment, and performance wise NiMH are catching up, that's why the RC world abandoned NiCd.

I was very suprised that the Sonicare toothbrush costing over $100 use cheap NiCd battery. And the new home phones still use NiCd. Many of the phone i used had the NiCd battery died. The NiCd in my current Panasonic phone died, and i didn't bother to buy the expensive replacement. I revitalize it with standard NiMH cells with a litter soldering work, and it's been working great with longer talk time

0roo is right. The reason NiCd is still in use for electric RC cars is that NiCd can deliver higher currents than NiMH but NiMH are catching up.

 

[NeoPTLD]

Originally posted by: FrustratedUser

Originally posted by: NeoPTLD
Many cordless phone and electric toothbrushes uses NiCd to these days. My Sonicare instruction recommends putting it on charger after each use.

I don't find any reference about modern NiCd batteries being immune from memory effect and I think its unavoidable with NiCd technology.

Why do they still recommend you to charge it after each use?

Because most of them use NiMH batteries and they don't suffer from the 'memory effect'.

No, Sonicare continues to use NiCd.

 

[Muse]

Originally posted by: Jeff7

Originally posted by: NeoPTLD
Many cordless phone and electric toothbrushes uses NiCd to these days. My Sonicare instruction recommends putting it on charger after each use.

I don't find any reference about modern NiCd batteries being immune from memory effect and I think its unavoidable with NiCd technology.

Why do they still recommend you to charge it after each use?

Cordless....maybe some of the 900Mhz/2.4GHz things do; cellphones use Li-ion, at least mine does. I imagine that a lot of companies might use Nicad either to get rid of old inventory, or else because it's cheaper. NiMH should be replacing NiCad; that's what I've done at home. Much better lifetime, and they can charge faster. Heck, I even ripped apart my ailing Dustbuster and replaced its NiCad batteries with NiMH's, and it runs much longer than it did when it was new.

This "memory effect" is sounding more like a renamed version of either "overcharging" or "deep discharge."

I don't recall my Sonicare instructions recommending recharging after each use. My handles (include the batteries), have a feature where when they reach the state where they require recharging, they beep for several seconds at the end of a particular 2-minute usage. That alerts me that recharging is required, and then I do not use that handle again until I do recharge it. I think I get around 25 2-minute brush cycles (once a day) on a single charge. It happens that I have two handles, so when this happens I charge the_other_handle (it takes about 22 hours to charge, so it's ready when I do my daily brushing next day). Both handles seem to me to be in fine shape, and it's been about 5 years since I bought this set, and always used this regimen.

The current use of Nicads cannot be solely attributed to the corporations wanting to move out antiquated technology in lieu of supplying superior NiMH's (or Li-ion's). Nicads do not lose their charge as fast as NiMH, for instance. If you have a device that you don't use all the time, it may indeed run down much more from the attrition affect than from actual tool usage. I don't know the figures, but these batteries lose their stored energy around 1% a day, but Nicads definitely lose their energy in this manner quite a bit slower than NiMH's, I'm told. NiMH's are more expensive, so that's one reason to go with Nicads, but I also lean toward Nicads in a situation where I don't use the tool frequently. NiMH's give about 60% more energy before they need recharging (sometimes more, I think), not counting the faster shelf power loss factor. All these factors come into consideration when you are choosing a battery. Nicads used to have the memory effect, but that's said to be mostly history.

Another thing to consider is that modern Nicads evidently are apt to last longer than NiMH's. I've seen claims that certain NiMH's might be rechargeable up to 1000 times, but usually they claim up to 300 times. Nicads, I believe, are thought to be rechargeable a fair amount more than NiMH's, at least the newer ones.

 

[Muse]

Originally posted by: mooncancook
The NiCd in my current Panasonic phone died, and i didn't bother to buy the expensive replacement. I revitalize it with standard NiMH cells with a litter soldering work, and it's been working great with longer talk time

The battery pack in my Panasonic cordless phone died rather soon after purchase and I contacted the company for warranty relief and they sent me a newer model phone. I think the first phone probably had Nicads, not sure. I followed the manual's recommendation of NOT leaving the handset on the charging base based on their indication that battery life would be extended if I did not do so. It didn't seem to have helped.

The replacement phone has NiMH batteries in the pack and again, the manual recommends not leaving the handset charging for maximum battery pack life, and again, I try not to. What I do is turn the phone around so it doesn't make contact and charge. However, the battery pack runs down pretty quickly in that state and needs recharging at least once a week, so I have to remember to turn it around and recharge it! So far, though, it hasn't died like the other one did. I've had this one over a year now.