Roche F22 and batteries?

I just received my Roche F22 with extender tube and had a question about batteries? I bought this since I had a bunch of 26650 batteries sitting around, all of them are unprotected. So here is my question is it dangerous to use this light with 2 unprotected 26650 batteries???

Depends on your definition of dangerous. >) Just make sure the 2 cells are well matched and are the same voltage and you should be fine. Also make sure you don't overdischarge them.

When you say overdischarge them do you mean running then down until they are empty?

Yep, I would recharge them at around 3.6 volts, but they should be fine down to 3.0 volts.

Im curious on this one.
What happens if you over discharge the batteries
I always hear about unprotected being dangerous, but I have always pondered what “dangerous” actually is.
Is it a little “pfft” with a little smoke or is it a thermal nuclear meltdown.

When ever I buy a multi cell(eg skyray king) light I usually a set of batteries to go with it so they all get the same discharge-charge.