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How to recharge these batteries? Answered

I took apart 2 cordless drill batteries and there were 13 cells in each one, which were Ni-Cd 1.2 volts each. Also there were the numbers C DE35ND on them if that helps at all. I cut 3 off in order to form a 12v battery (it was originally 15.6v) but I dont know how I can safely charge it. I no longer have the charger that went with the drill, but I was wondering if I can just use a wall adaptor to charge them or do I need a better charger? All comments and answers are greatly appreciated!!!

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steveastrouk (author)2011-08-03

Nicad charging relies on a constant current technique. Fidn the capacity of the batteries, in Ah, and divide the number by 10 for the charging current. So a 1Ah battery needs 0.1 A to charge it for 10 hours.

If you use a circuit like the one I attach, and set the resistor you need =1.22/ charging current, you'd be good to go - provided the current is less than 1 A or so.

I hesitate to suggest another way, because they rely on being able to measure battery temperature to detect when the battery is charged. Charging at 1/10 C is a safe method, and you can leave the batteries on charge occasionally without harming them. Faster rates are actively dangerous, without proper control.

Steve

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Vyger (author)2011-08-03

I bought a set of new batteries and a charger for them on E bay. There is a guy who specializes in just batteries and chargers.
Your drill will run on 12 volts but not very well, just barely.
Just get a new charger and battery. If its to expensive then get a new drill. Sad to say but sometimes a new drill kit will cost less than replacement batteries.

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Electronics Man (author)Vyger2011-08-03

thanks for the answer, but I no longer want to use them with my drill, thats why I turned them into 12v batteries. I just want to have a rechargable 12v battery pack that I can easily charge.

Thanks for the answers!

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rickharris (author)2011-08-03

I changed my cordless drill battery - dead - for 2 x small 12 volt lead acid battery - Works well and I charge with my car charger.

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