NiCad battery rejeuvenation - TTORA Forum
 
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post #1 of 4 (permalink) Old 08-16-2008, 06:28 PM Thread Starter
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NiCad battery rejeuvenation

I tried to buy some replacement batteries for my dated 9.6V Dewalt drill/drivers. I got pissed off when I found they were $40 each, since the original kit with two batteries was only $69. (Many years ago.) So this is intended to alert you all

I have four batteries, since 5 years ago it was also cheaper to buy another kit than replace the batteries at that time.

I was down to one battery that seemed to be about 50% - the others were at 7-8VDC when the charger quit - a sure sign of a shorted cell or two.

After some google searches I opened the cases on the 3 cripples, found the shorted cells and shocked them with high current from another battery to kill the dendrites. One cell took three shock treatments, but they appear to all be fully recovered to original capacity.

DeWalt ought to be sued for not making a battery charger / rejeuvenator for these $40 units.

Wilf's page seems to be a good resource for properly treated batteries. You may need to "get Medieval" on some old, mistreated batteries. (Troy, you need to see if you can revive your Dremel this way. I can't remember if it's NiCd.)

If your battery won't charge near to the nominal voltage, then the shock treatment is necessary followed by a 24 hour charge and maybe some deep discharge/charge cycles. If the short reforms shock the bad cell again. Resort to extreme prejudice if necessary - get that sucker hot with short pulses of very high current. If you fry it - Hell it was dead already, right? I shocked a single cell using a full 7 cell string three times before it finally recovered.

If the battery capacity is low, but it charges to nominal voltage, then you need to discharge it slowly to 0.5 VDC/cell (my 9.6 VDC power pack is really seven 1.35 VDC cells.) My second drill kit came with a flashlight that gives a nice slow discharge. Open the battery case and make sure that the lowest cell does not go below 0.4 VDC when deep discharging like this. Then recharge the whole pack. You may need to do several deep discharges to fully revive a battery.

The good news is that the recovery is supposedly permanent if you treat the battery correctly from now on. But who dos that? Mine often go months between uses.

more battery advice

still more battery advice

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Last edited by Don_G; 08-17-2008 at 05:14 PM.
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post #2 of 4 (permalink) Old 08-17-2008, 10:46 PM
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Hmmm....interesting. Not sure I would be up to tackling that challenge. Things like batteries, enclosed waterproof casings, chemicals, electronics.....not my thing. Nice work, though!

I've never been a person to say, "I can't" so I really admire that, and can relate. Faced with the same situation, I would probably do the same thing, even though I don't really like the idea of it.
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post #3 of 4 (permalink) Old 08-18-2008, 08:08 AM
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I've always hated nicad batteries because their life spans seems to suck if you're not 100% meticulous with the charge/drain/charge cycle... and even then it's not great.

I'll have to read this more carefully and give it a try on some of my dying batteries.

de∑gen∑er∑ate

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post #4 of 4 (permalink) Old 08-18-2008, 08:11 AM
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Thanks Don. I've got two nearly dead Dewalt batteries myself. This is great info!

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