It doesn't matter what size they are, any li-ion can overheat and burst into flames.
Since they're unprotected, it means they don't have the built-in shut off when it reaches a certain voltage. Most are somewhere around a 2.5v cut off. If your unprotected battery goes under a certain voltage and you then recharge it, it can become unstable.
The whole point of having protected batteries is to protect them from going over their normal charging voltage, or over-discharging. The PCB also protects against short circuits because it's designed to shut off power if such a thing happens.
I wouldn't use them if you're not 100% certain you can keep a steady watch on it's charge.
Oh my.... This battery fear is driving me nuts!!!!!!
Most 10440 batteries will not say protected on them... They are to small to get all that writing on it...
To check and see if the battery is in fact protected you should see a strip inside the plastic wrapping of the battery that runs from the negative end to the positive end...
Most, if not all batteries that have exploded were unprotected batteries that were used in series... Ie... one on top of the other (2 total) in the mod...
I have yet to read ANYWHERE where a single battery, protected or not, has blown....
My .02 on the whole terrified of batteries thing....
Kris