Few Question about the Unprotected Cells.

Fallingwater said:

Zeroed LiIon cells can be rescued, but the amount of damage they suffer depends entirely on how long they've stayed under their safe voltage.

If they're left zeroed for too long they may still accept a charge, but they'll develop very high internal resistance and self-discharge.

As for whether they can damage a light... well, it's usually paired primary CR123s that tend to burst flashlights. So far I only remember one thread of LiIon cells venting inside a light, and everything that happened was a very hot battery tube. Not good, but not a grenade either.

That said: just zeroing the cell inside the flashlight is very unlikely to cause damage. Zeroing, recharging, and then using at full power again increases the chance of eventually having the tailcap shoot off your light...

From my experience and from what I've read here, you have to mistreat LiIon cells pretty badly to get them mad at you. Many people tend to be paranoid about them and treat 18650s like armed grenades ready to go off at the slightest provocation, but so far I've seen surprisingly little evidence of their danger.
You *can* get them to vent if you really try (puncture one and you get a nice firework), but they seem to be pretty resistant to casual damage.

Note that I'm not advocating the careless use of unprotected cells. Actually, always use protected ones if you can, so you can't overdischarge them. Just because I've seen few people reporting flaming LiIon cells doesn't mean you can't be next.

By the way, the really dangerous cells are unprotected, high discharge Lithium Polymer ones, like those for RC models. Those are known for bursting in a fireball if you look at them wrong, and they've caused several members over at the RCgroups board to lose very valuable possessions, including cars and homes...

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