18650 Li-ion Smoking

Hi everyone,

I've had a rechargeable flashlight for a while that required a new set of two 18560 Li-ion batteries. I didn't take note of the way the original batteries were inserted so I inserted the new batteries in series instead of parallel and one of the batteries started smoking vigorously and completely shrunk the negative contact springs after glowing red. After retensioning the springs, I got the device working again with the new batteries but decided to get some new batteries. I've inserted batteries wrong way around many times in my life but nothing happened. Is this expected behaviour because of my ignorance or stupidity? Should there have been some sort of polarity protection?
 
Not sure if I understood you correctly, but It seems like you reversed one of the batteries such that they are anti-parallel instead of parallel. The high voltage difference between them induced a circulating current between them. The magnitude of that current rised to a high value due to the low resistance of the contacts leading it to glow from the heat.

Yeah, polarity protection should have been there but some designers remove it to avoid the 0.7 v voltage drop of the diode.
 
Not sure if I understood you correctly, but It seems like you reversed one of the batteries such that they are anti-parallel instead of parallel. The high voltage difference between them induced a circulating current between them. The magnitude of that current rised to a high value due to the low resistance of the contacts leading it to glow from the heat.

Yeah, polarity protection should have been there but some designers remove it to avoid the 0.7 v voltage drop of the diode.
That's exactly what happened. Are there not safety standards for this type of thing?
 
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