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NiCd battery for power tool won't charge
Bill Ketchel

Total Topics: 2
Total Posts: 9
I just wanted to pass along a little trick I learned this weekend to "revive" a seemingly dead NiCd battery. I have an old Ryobi 18V NiCd that wouldn't take a charge. I would put it in the charger and it would trickle charge (overnight) but would never click into fast charge mode. My research said this was "dendrite growth" within the battery cells. These are basically little micro-shorts internal to the battery.

Well, the solution is to blow away the dendrites using a large power source. So when I got to work this morning I took one of our very beefy power supplies, set the voltage to about 10V, current limit to around 8A and then jolted the heck out of the battery. It worked! It's not fast charging normally and I've tested it in the router and my old torque has returned. It's like having a brand new battery!

Just thought I'd pass this tip along in case you (like me) don't want to spend $50~100 on a new NiCd or Li-Ion battery for your tool.

BTW, this ONLY WORKS ON NICD. Li-ion is different chemistry and when it conks just have to buy a new battery. You can't shock it back to life.


Jun 30, 08 | 6:57 am
Bill Ketchel

Total Topics: 2
Total Posts: 9
Correction....I set the voltage to 20V. The voltage needs to be set a little higher than the rated battery voltage. It's also important that you have something that can deliver a lot of current. When you do this, you don't leave the power supply connected for long......maybe 1/2 second. Just long enough to blow the dendrites away.

I read you can also use a charged capacitor to do you're basically delivering a high current pulse.

Jun 30, 08 | 7:00 am
Dennis Weatherly

Total Topics: 73
Total Posts: 651
If you have someone in your area that flies electric powered RC model airplanes, check with them to see if they hace a NiCD high current charger around. My old AstroFlight 112 will deliver up to 5 amps into a battery pack made of 6 to 24 cells. That's 7.2 to 28.8 volts! We charge NiCD packs at this kind of rate all the time and discharge them at even higher rates. The secret to NOT frying the battery is that these chargers have Peak Detection systems in them that shut down the charge at the proper time.

I'll re-iterate Bill's warning about other battery chemistries...DO NOT try this with Nickel Metal Hydride or Lithium cells! These cell chemistries do not develop this kind of problem.

Jun 30, 08 | 11:29 am
Kevin Sjostrand

Total Topics: 84
Total Posts: 981
I have thrown away at least a 1/2 dozen of those Ryobi 18v battiers in the last 2 or 3 years.......wish I had known this before!
That sounds like a great price for a cordless router. I'll have to check my local HD.

Jun 30, 08 | 11:38 am

Total Topics: 10
Total Posts: 22
Hi Y'all We have a digital read out on our MIG welder at work. You can set it above the rated voltage of the battery as stated above. Build a set of jumper wires to insert in the battery terminals, strip the other end and connect 1 lead to the welder ground. Turn the wire speed on the welder to 0 ,then touch the stinger to the other jumper. A couple quick pulses are enough. Works like a charm!

Jul 20, 09 | 4:22 pm

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