NICD vs NIMH batteries

I have a portable CD player which specifies using either alkaline or rechargeable NICD batteries .
Should it be acceptable to use NIMH also?
I am wondering whether the charging rates are so different for the two rechargeable types that the NIMH, or the charging circuit, might be damaged.
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It will work ok on them as they are very similar to Ni-Cad.

The charging systems are different. You could charge them using an external charger, though, and simply swop them.
High capacity Ni-Cads aren't that much behind standard NiMH, and are slightly cheaper. They also have a longer service life if charged correctly.
--
*I used up all my sick days so I called in dead

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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On Tue, 27 Jan 2004 00:15:02 +0000 (GMT), Dave Plowman
<SNIP>

Do you mean I should't charge NIMH on my NiCd charger?
Peter
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wrote:

There shouldn't be any differences between them as long as you aren't using a higher voltage than the battery needs to take its charge.
"http://www.batteriesplus.co.uk/acatalog/Batteries_Plus_Chargers_and_Power_S upplies_5.html"
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Correct. Although chargers that do both exist.
That's not to say a Ni-Cad charger won't work *at all* with NiMH - it will simply shorten their service life.
--
*I didn't drive my husband crazy -- I flew him there -- it was faster

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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A NiCd charger will work but it may not detect that the NiMH battery is full and simply continue charging, which is no good.
Quote from
http://www.greenbatteries.com/documents/Battery_Charger_FAQ.htm
" Can I use an older NiCd battery charger to charge NiMH batteries?
The answer to this question depends on the type of NiCd charger. Depending on the type of NiCd charger you have, the older NiCd charger may undercharge NiMH batteries (most likely), it may overcharge them (less likely), or it may charge NiMH batteries properly (but it's not likely to do so automatically and could take a very long time). Let's take a look at the three cases.
Many of the older NiCd chargers are the simple timed type charger which will charge batteries for a fixed amount of time and then shut off. Unfortunately, since NiCd batteries have a much lower capacity than NiMH batteries, the timer is likely to shut off long before the NiMH batteries are fully charged. This won't harm the batteries, but the NiMH batteries won't be fully charged since the timer will have stopped the charge cycle too soon.
Also common among older NiCd chargers are the so called "overnight" chargers which charge batteries at a low rate as long as the charger is plugged in. This type of charger can fully charge NiMH batteries, but it might take a very long time to do so. It's possible that an old NiCd charger could take as long as 48 hours to fully charge new high capacity NiMH batteries! This type of charger is not likely to damage NiMH batteries unless the batteries are left in the charger for weeks at a time, but it may not be very convenient to use. If you have this type of charger you can get an idea of how long you'll need to charge your batteries by using the calculator found above.
The final possibility is that the older NiCd charger is a rapid charger that will charge NiMH batteries but will not have the necessary circuitry to stop the charge cycle once the NiMH batteries are fully charged. If the NiCd charger is designed to charge batteries in less than two hours it may be this type. In this case the risk is that the older charger will overcharge NiMH batteries. This will be apparent if the batteries get very hot during the charge cycle. (It is normal for NiMH batteries to get warm as they become fully charged, especially in a rapid charger). If the NiMH batteries get too hot to handle and stay that way for more than 20 or 30 minutes, then the NiCd charger is most likely overcharging the NiMH batteries and may shorten their life. You would be most likely to encounter this type of charger if the charger was designed for rapid charging radio control (RC) vehicle batteries. We would recommend that you not use an NiCD rapid charger to charge NiMH batteries. "
/Clas-Henrik
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One thing that hasn't been said is that NiCd cells retain their life best if they are discharged almost fully before recharging. They collect what is known as the memory effect if charged when half discharged and tend never to have their full capacity thereafter. NiMH cell do not hav this characteristic and can be recharged at any time.
rob
snipped-for-privacy@hotmail.com (C-H Gustafsson) wrote in message

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Not that old chestnut again, please!!!
The memory effect in NiCd cells is *extremely* unlikely to occur in normal domestic usage. It only occurs when NiCd cells are repeatedly (i.e.hundreds of times) recharged and discharged to exactly the same levels. The effect was noticed in NiCds used on a satellite which got recharged very regularly each day when the sun rose.
The only reason that dicharging a NiCd completely may help is that a full charge will not then overcharge it. It's overcharging that makes most NiCds fail before they should.
--
Chris Green

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In uk.d-i-y, snipped-for-privacy@isbd.co.uk wrote:

Indeed, it refuses to die, and as a powerful myth finds its way into instruction sheets for a fair bit of consumer gear. As you say, one partial truth is that by telling you to fully discharge your cells before attaching them to their cheap chargers, and telling you to run the cheapo for a limited time, mfr's hope to reduce one of the likely causes of overcooking - leaving an already-charged cell on (non-tiny) charge. Simpler than incorporating a charge-control IC and switching tranny into the circuit, and saves valuable component cost ;-)
Stefek
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Trouble with this approach is that if it's a drill etc and you run the batteries *completely* flat by leaving it on 'till it stops, there's a very real danger of one or more cells charging in reverse. The best way is to only run them down until the performance is impaired.
--
*What hair colour do they put on the driver's license of a bald man? *

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Rob Graham wrote:

Urban myth Rob.
It happend once with a very regular charge/discharge regme on some spacecraft. No one has ever really demonstrated it with random charging.
Nicads lose charge anyway over about a year. Or faster. NiMh are dead within a few months if not charged. They recover tho.
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Peter wrote:

Not if its a fast charger and doesn't know about NiMh. OK on a trickle tho.

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snipped-for-privacy@invalid.com wrote:

Its possible. Nimh need slower and more critical charhing on 'fast charge' (about 1 hr max for NiMh.
But the chances are its a trickle charger anyway. So NiMh will be fine.
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