I charged my battery pack below zero, is it now a fire hazard?

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Jul 15, 2013
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I just learned it creates lithium dendrites that may tear the barriers and can cause a fire. How real of a problem is this? Should I throw away the battery or it should be ok to keep using? I’m no DIYer, or engineer, but I sincerely regret making such a silly mistake. Any where I can bring it in for testing in or nearby NYC? Thanks!
 
there's no way to know what physical damage exists inside cells without physically destroying them to open them up and examine them (usually by some form of microscopy).

if you had access to individual disconnected cells you could run internal resistance testing to compare to spec sheet values for the cells, under load and without load, but this requires disassembly of the pack for that access, and that risks damage / shorts / etc if not done carefully, and reassembly of the pack afterward requires tools, parts, and knowledge that may cost more than the pack itself is worth, especially if it's older.

by "charged...below zero", do you mean that the battery was discharged down below 0v, so it is now a negative voltage? If so, that's probably damaged in a way that i myself would not want to risk re-use.

if instead you mean that you charged it below 0 degrees (c? f? etc?) then the results may be less predictable, but more details are needed. was the pack actually completely cold-soaked, so that it was internally at that temperature? or was that just the ambient temperature, and the pack itself was normal in-use temperature?
 
I just learned it creates lithium dendrites that may tear the barriers and can cause a fire. How real of a problem is this? Should I throw away the battery or it should be ok to keep using? I’m no DIYer, or engineer, but I sincerely regret making such a silly mistake. Any where I can bring it in for testing in or nearby NYC? Thanks!
At 0C, it all depends on the charge rate.

If you charged at the standard 0.1-0.2C, you're likely fine if you don't do it more than once.
 
I meant below zero C ambient temperature, as in freezing. I don’t think it was done more than say half a dozen times. It appears to hold the same charge for months and I have charged it since, without noticing any degradation in performance.

It’s a small pack for a skateboard 10s2p, so probably reaches ambient temperature relatively quickly and it was outside for quite a while being used, before sitting there charging. I don’t have any way to tell the battery pack temperature.

I wish there was a simpler method to test it.
 
yep I went down past zero to negative volts once
 
As long as it works fine, nobody will be able to tell if it has any damage or not. It's generally known that li-ion shouldn't be charged at negative temperatures, and shouldn't be over-charged or discharged too deeply, but many of us have done so without any sudden failure. Maybe it will just last a bit shorter that it should.
 
yep I went down past zero to negative volts once
Then that's a pack that should be replaced, if you want "certain" safety, since there could be undetectable damage to cells that could unpredictably cause a catastrophic failure that could include a fire. (even if the pack appears to be working correctly for now).
 
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I meant below zero C ambient temperature, as in freezing. I don’t think it was done more than say half a dozen times. It appears to hold the same charge for months and I have charged it since, without noticing any degradation in performance.
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I wish there was a simpler method to test it.
If it is performing exactly the same before as after, it's *probably* not changed in internal cell properties. But the only way to know that for sure would be to have tested the cells individually beforehand, then retest them individually afterward, for all the possible properties. This still wont' tell you about any damage that doesn't change the specific tested properties...but it's likely those will catch any serious change.

Unfortunately the only way to know the true complete internal condition of the cells is a destructive disassembly...this is about like a doctor doing an autopsy on every patient that walks thru the door to see if they have a cold, though. ;)
 
I won’t take the risk. Thanks guys. What should I do with the pack? Anyone here want it?
 
If it was outside being used before you charged it then that sounds like the ideal situation for cold charging. Using it heats up the battery so it may have been just fine when you charged it.

If it sat out in the cold such that the cells were internally below zero all then I would be more inclined to think it has some damage.
 
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