Charging mishap, warning

brandocommando

Enlightened
Joined
Mar 10, 2011
Messages
437
Location
Oregon
So I have been recharging batteries for a long time, (used to race RC as a kid.) But I have not done much charging using the alligator clip/magnet technique however, and I sort of goofed yesterday.
I was charging my 2 brand new IMR 18350's in parallel and after the charge was completed, I started to remove the batteries. I removed one, and was putting it aside when the 2 magnets (very powerful 1/4 in X 1/4 in) on the now empty aligator clips snapped together... thus causung a short on the the remaining battery!!
I immediately disconnected it, and it saw a short for 1 second or less. I tested the voltage and it was 4.1-ish volts (I can't remember exactly) instead of the 4.2V it would have been if not for the short.

Did I ruin this battery???

I used it last night just fine and I am charging it again now, (in parallel with the other one again.) It is charging just fine and is not hot at all, it's cold in fact because it's out in the garage.

So, let this serve as a warning to others, watch out for those magnets!
 

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
11,212
Location
Tulsa,OK
You are probably fine if the battery did not get hot and only discharged 1/10th of a volt. If you left it on long enough to melt wires and the insulation off the battery you may have a fire or damaged cell.
 

Battery Guy

Enlightened
Joined
Apr 28, 2010
Messages
807
Location
Portland, Oregon
Did you "ruin" this cell? In my opinion, the answer is "no".

Did you "hurt" this cell? In my opinion, the cell has probably been degraded to a small amount in performance. Had you measured the capacity and internal resistance before and after the short circuit event, you would probably have been able to detect a decrease in capacity and an increase in internal resistance after the short circuit event. The extremely high short circuit current (probably >50 A in an IMR 18350) can result in degradation within the electrode winding itself. I recently did some tests looking at the potential impact of a brief low resistance short circuit on the performance of a lithium-ion cell, and in every test I did there was a measurable permanent degradation in performance.

That being said, I would say that you can continue to use this cell. Most of the tests I have done show a measurable, albeit small, change in cell performance with one short circuit event similar to what you describe. The real problem is when the cell is exposed to repeated short circuit events, where the degradation can be cumulative.

Cheers,
BG
 

brandocommando

Enlightened
Joined
Mar 10, 2011
Messages
437
Location
Oregon
It was an accucell6. It has all sorts of protection stuff on it but, the charge had just finished so the charger was not doing anything really. Luckily the battery is doing fine, and like BG said above, I think I just caused some very minor damage to the cell. It is now coming out of my flashlight with a 1/100th of a volt difference compared to the other one after use.
Thanks for the responses so far.
 
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