Yes agree, unfortunately I did not see what happened. I presume that to be the case even though nimh have been charged issue free on the C4-12 previously. But yes, just use my opus BT c3100 for my Nimh cells going forward. Although not likely to cause a fire themselves, sat next to cells that can though. Also a little liquid did leak from the case, potential electrical issues if it got into the charger.
It's good info, in any case. I sometimes use an all-chemistry charger to charge Eneloops, but your experience has made me rethink that, and stick with NiMH-only chargers from now on. Or, at the very least, feel them part-way through the charge to make sure they're not too hot.
It seems you may misunderstand my intent. To clarify: my safety recommendations are not intended to be 100% safe (impossible). Rather, they are in fact meant to be reasonably safe given the best of our knowledge. If you want FUD then you can follow reputable manufacturer's warnings that loose Li-ion cells should never be used by consumers (e.g. see the
Sony cease and desist letter). More experienced users like you or I may be comfortable that we can safely manage less conservative practices, but that doesn't mean that we should recommend those riskier practices to the masses - who may lack the knowledge, discipline, etc to properly handle those risks.
I could be wrong, but the OP doesn't seem inexperienced with lithium-ion cells. He's been at it for 10 years, by the sounds of it. Everyone should be made aware of the risks, but that shouldn't mean over-emphasizing the danger.
There are varying degrees of managing the risk. Use only protected cells, use only new cells, etc. But older, unprotected cells can be used safely, as long as you do some basic testing to make sure they're still okay. And, don't over-stress them in a high-drain application.
I certainly wouldn't use an old cell for vaping. But I have no issues with using old cells in 500-1000 lumen lights. More than 1000 lumens, an old cell isn't going to give good performance anyway, and safety does become more of a valid concern.
FWIW, the only 18650 cell I've had a problem with (from a safety perspective) is a brand-new Samsung 30Q cell. Very high self-discharge. I don't use it, except for occasional experiments and testing, and I keep it in a tin can for safety.
All my old cells from laptop pulls (some 10 years old), work fine. Their capacity is limited, but they make good back-up cells in case I don't have a new cell charged up. Since they're already old, I have no issues keeping them fully charged even if it ages them.