I'm just happy that nothing more 'unpleasant' resulted from its failure. That's the big thing, and that's great. It's also good that you visually inspected it and detected an issue when you suspected one.
I know little about cells / batts, nor chemistry, so I'll leave that for others to speak to or speculate about. All I do know is that Li-ion cells have more failure modes besides the more benign ones like loss of capacity with cycle count, etc. There are others which are less progressive, more acute, unpredictable, and potentially problematic when they occur. Some likely result from tiny deviations / defects from the manufacturing process(es), which are likely difficult or impossible to detect at that time, and which can likely result in failures which could be asymptomatic to the user and might not be detected by provided stats or conventional testing.
Some of the instances that make the news likely involved users who were less astute, either didn't notice symptoms or didn't pay attention to them if they did, and the failure was allowed to progress to a 'catastrophic failure' point. Fortunately you were paying attention, and your story was good for me (and perhaps others) to hear. Thanx.
I'm glad it wasn't worse but the mental image of that kid at the store is hilarious.
