USB charge an unprotected battery inside Nitecore MH10 flashlight dangerous or safe?

I tried but I could not google myself out of this question.

Say that I put an unprotected 21700 cell in such a flashlight and charge it via the lights USB port. Will it stop in time or does it expect a protected cell to call it quits? I am not afraid of undercharging but rather of overcharging.

Some sort of disclaimer: I would prefer to use unprotected cells for the usual reasons. The light has a warning light when the cell is getting low and I am quite sure it will dim well before something (in a worst case scenario) blows up. But when there is no socket around, I will charge it with my power bank with the cell in the light instead of a charger.
It just so happens that most high end chargers/analyzers do not support protected 21700 cells which adds to my reasons to go unprotected.

I did a search and found this....


The MH10/MH12 have a physical reverse polarity feature in the head, with the modern Nitecore design that allows "wide button top" cells to still work in the light. True flat-tops (where the positive contact is below the wrapper) won't work, but all my cells with a slightly raised contact worked fine.
Nitecore MH10, MH12, MH20 (XM-L2 1x18650/2xCR123A) in ...

www.candlepowerforums.com/vb/showthread.php?409127-Nitecore-MH10-MH…






So while this may not answer your question completely, if you were going to buy
an unprotected cell that is flat top according to the above it won't work.

I don't know of any light with a USB charger that requires protected cells. AFAIK, they all use the same basic CC/CV charging chips, which are meant for unprotected cells.

Its not only about reverse polarity protection which can be physical as well as simple mosfet. If that happens, charging circuit wont probably even start charging. But there is potential risk, when the charging circuit fails and fails that way so it allows futher charging. Cell would be massively overcharged and can heat or vent.

Protected cells are there for exactly this reason. Nobody expect charging circuit to fail, but it can happen (like every consumer electronics have failures), so its good to have another protection (in the cell) which prevents all bad scenarios. Cell's protection is also good to prevent short-circuit if anything in the flashlight circuit fails. Undervoltage is not dangerous, it can only destroy the cell itself.

Nobody says you must use protected cells. If you know the dangers and how to prevent or minimalize them, you should be fine. But for normal consumer, (quality) protected cells are the must.
Its like saying you do not need fuses in your car. Sure you can hardwire but its dangerous when something goes wrong.

Just be sure to keep wraps in perfect condition, if you use protected cells. The only thing separating the positive strip they add, and the negative side of the battery can, is an extremely thin plastic shrink-wrap. If the inner wrap gets damaged, the battery can short-circuit itself.