Power tool batteries; tried to be clever and failed

[dickm]

I have the usual collection of tired or non-functional deWalt 18V batteries, and thought it might be an idea to try cannibalising a couple together, replacing dud cells in one with apparently OK ones from the other. Got it all back together, but when trying to charge it, the charger gave the "battery fault" light after a couple of seconds. Tried in a different charger, and it apparently charged up, but only got to 14V.
All the cells that are in the reassembled battery seem to charge to a similar voltage, and none seems in any way different. Wondered if the thermistor might be faulty, but both seem to have similar characteristics when tested.
Any suggestions, other than "don't bother"?

 

[MMUK]

What technology are they? Lithium?

 

[dickm]

NiMh.

 

[Ed Bray]

A good thing to try with Nimh or NiCad batteries is to shock them back to life. There are videos of how to do it on YouTube, I have done it with two different makes of batteries and it worked with both.

 

[dickm]

Would the external automatic defibrillator they have in our local pub do the job??
Yes, had seen some of those vids, but haven't worked out what's in the workshop that could be used to provide suitable voltage.

 

[Ed Bray]

Would the external automatic defibrillator they have in our local pub do the job??
Yes, had seen some of those vids, but haven't worked out what's in the workshop that could be used to provide suitable voltage.

I used some other 18v batteries I had and wired them in series, you could do similar with 3x car batteries.