NICAD cell problem - dendril?

I suspect that I have cells with dendrils in my three DeWALT DE9074 12V 1.3Ah Nicad packs. These packs have been used with a DeWALT screwdriver
and recharged no more than 50 times. Now the DeWALTcharger is indicating faulty battery and will not start the charge. If any of you have checked the price of replacement DeWALT batteries you will understand why I am trying to repair them.
After opening the pack I measured the voltage and current in each of the ten cells. Voltage is only m.v. +ve and current 8 microamp which is expected as the packs have been idle for 6 months.
Next I connected a "2V 0.5A" simple charger to one of the bad cells. Charging readings at switch on were 0.638V and 1.11A. After 1 hour the readings were 0.577V and 1.03A. There was no rise in cell temperature.
I disconnected the charger and could not measure any voltage or any current in the "charged cell"
Why is there a charging voltage and current but no measurable output? Is this a symptom of dendrils?
Beemer
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|I suspect that I have cells with dendrils in my three DeWALT DE9074 12V | 1.3Ah Nicad packs. These packs have been used with a DeWALT screwdriver | and recharged no more than 50 times. Now the DeWALTcharger is indicating | faulty battery and will not start the charge. If any of you have checked | the price of replacement DeWALT batteries you will understand why I am | trying to repair them. | | After opening the pack I measured the voltage and current in each of the ten | cells. Voltage is only m.v. +ve and current 8 microamp which is expected | as the packs have been idle for 6 months. | | Next I connected a "2V 0.5A" simple charger to one of the bad cells. | Charging readings at switch on were 0.638V and 1.11A. After 1 hour the | readings were 0.577V and 1.03A. There was no rise in cell temperature. | | I disconnected the charger and could not measure any voltage or any current | in the "charged cell" | | Why is there a charging voltage and current but no measurable output? Is | this a symptom of dendrils? | | Beemer | Sorry, I should have said that there were three bad cells in the first battery I checked. The current from these was zero i.e. unmeasurable.
Beemer
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There are companies that rebuild batteries. This could be extremely handy for folks who own older tools where batteries can no longer be bought new.
You seem to be handy with this stuff, so you'd probably save time and money rebuilding your own. A quick Google search turned up:
http://www.batteriesamerica.com/newpage3.htm
I haven't personally dealt with this company before, so I can't vouch for them, but there are more out there. Many stores sell standard sized rechargeable batteries, including sub-C types, with tabs already soldered in place (highly recommend!) which are intended for battery packs such as yours.
You might be able to bring individual cells back to life, as long as there's no damage from reversed voltage, which is quite possible if they've been sitting around for a long time without being used. Connecting to a slow dumb charger for a time might do it. I've had some success doing this, but the batteries never seem to last for long.
If it were me, I'd just rebuild the pack. You will most likely get better quality batteries.
CS

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| > |I suspect that I have cells with dendrils in my three DeWALT DE9074 12V | > | 1.3Ah Nicad packs. These packs have been used with a DeWALT | > screwdriver | > | and recharged no more than 50 times. Now the DeWALTcharger is | > indicating | > | faulty battery and will not start the charge. If any of you have | > checked | > | the price of replacement DeWALT batteries you will understand why I am | > | trying to repair them. | > | | > | After opening the pack I measured the voltage and current in each of the | > ten | > | cells. Voltage is only m.v. +ve and current 8 microamp which is | > expected | > | as the packs have been idle for 6 months. | > | | > | Next I connected a "2V 0.5A" simple charger to one of the bad cells. | > | Charging readings at switch on were 0.638V and 1.11A. After 1 hour the | > | readings were 0.577V and 1.03A. There was no rise in cell temperature. | > | | > | I disconnected the charger and could not measure any voltage or any | > current | > | in the "charged cell" | > | | > | Why is there a charging voltage and current but no measurable output? | > Is | > | this a symptom of dendrils? | > | | > | Beemer | > | | > Sorry, I should have said that there were three bad cells in the first | > battery I checked. The current from these was zero i.e. unmeasurable. | > | > Beemer | > | > | CS,
Thanks for the link. I might giver this supplier a try.
Beemer
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CS,
Thanks,
Beemer
| > |I suspect that I have cells with dendrils in my three DeWALT DE9074 12V | > | 1.3Ah Nicad packs. These packs have been used with a DeWALT | > screwdriver | > | and recharged no more than 50 times. Now the DeWALTcharger is | > indicating | > | faulty battery and will not start the charge. If any of you have | > checked | > | the price of replacement DeWALT batteries you will understand why I am | > | trying to repair them. | > | | > | After opening the pack I measured the voltage and current in each of the | > ten | > | cells. Voltage is only m.v. +ve and current 8 microamp which is | > expected | > | as the packs have been idle for 6 months. | > | | > | Next I connected a "2V 0.5A" simple charger to one of the bad cells. | > | Charging readings at switch on were 0.638V and 1.11A. After 1 hour the | > | readings were 0.577V and 1.03A. There was no rise in cell temperature. | > | | > | I disconnected the charger and could not measure any voltage or any | > current | > | in the "charged cell" | > | | > | Why is there a charging voltage and current but no measurable output? | > Is | > | this a symptom of dendrils? | > | | > | Beemer | > | | > Sorry, I should have said that there were three bad cells in the first | > battery I checked. The current from these was zero i.e. unmeasurable. | > | > Beemer | > | > | |
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CS wrote:

Forget it! Never really works.

As if there WERE such a thing as a "better quality" NiCad battery! Your first mistake was buying something that used nicads in the first place! The person who "invented" nicad batteries needs his/her ass kicked from here to China. They are total pieces of crap and should be avoided/replaced/ substituted/ trashed if at all possible. They are the reason my wireless phone is sitting over there unused. I just keep putting new batteries in my electric screwdriver to keep it going. Of course I don't use it much so you seem to get about 3-4 screw jobs per battery set. Nicads are the screw job!
But once you are locked into the loop. Just keep buying new batteries and putting them in! Happy soldering. Compare to my Toro battery weed whacker with lead gel cells. Got it for about $5 at a garage sale 15 years ago and it's still going strong. Yeah, gel cells die too, but at least they have some lifetime.

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I have several Makita battery powered tools and in response to the above, I will state that I have gone through two sets of the new and improved nickle metal hydride batteries during which time the original USED set of nickle cadmium just keep on chugging along. I have periodically run the ni-cads down to near zero with a flashlight and that keeps them rejuvenated. I know many people dispute this, including Makita. I say it works based on experience. That and never using one until it is fully recharged have kept some of my batteries in (hard) service for over 8 years.
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Benj wrote:

You must be doing something wrong. Mine (NiCds and NiMhs) last for years and years. I suspect you are not using them on a regular basis and charging them properly.
Ed
<snip>
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