18650's in Series OK?

I have a Hound Dog with an MD4 body. I have been running on 4 cr123's. I've resisted running it on 2 18650's protected because there is some talk out there that 18650's in series can be a little dangerous. I think the Hound Dog would run much better on the 18650's. Is my concern valid?

28gauge said:

I have a Hound Dog with an MD4 body. I have been running on 4 cr123's. I've resisted running it on 2 18650's protected because there is some talk out there that 18650's in series can be a little dangerous. I think the Hound Dog would run much better on the 18650's. Is my concern valid?

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AFAIK, should run only protected cells in series to be safe. And monitor their voltages to make sure they are not substantially different: I'm guessing at least within 0.05 volts of each other, if not even more strict. Running Unprotected cells in series is dangerous. (I should say can be dangerous)

28gauge said:

I have a Hound Dog with an MD4 body. I have been running on 4 cr123's. I've resisted running it on 2 18650's protected because there is some talk out there that 18650's in series can be a little dangerous. I think the Hound Dog would run much better on the 18650's. Is my concern valid?

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No problem running the 18650's as long as both cells are matched (both the same capacity and the same level of charge). In other words whenever you change out cells to recharge.........recharge both.

edit: I'm not that familiar with that particular light and so I may have spoke prematurely. However what I mentioned is the consensus for other dual 18650 lights.

Yes, your concern is valid, although arguably running 4x lithium primaries in series may present potentially even greater risk(s)

archimedes said:

Yes, your concern is valid, although arguably running 4x lithium primaries in series may present potentially even greater risk(s)

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+1... if you haven't had issues using 4 CR123, you will be fine with x2 Li Ion. Just use "married" batteries like you most likely have been doing with x4 CR123.

hotlight said:

Just use "married" batteries like you most likely have been doing with x4 CR123.

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28gauge,
One more suggestion: Whenever you use "married batteries" - every time you pull them off the charger - check them with a digital multimeter, to make sure that the voltage is close. Don't assume that because they have a history of having closely matched voltages coming off of the charger at the same time, that they will always be that way.

I am currently using three protected 18650's in a LEEF c to c tube. Just monitor the voltage before and after a charge. I do not mix and match batteries. These 3 batteries will stay as a set.