Probably a non-user-serviceable Li-ion. I dislike that trend, especially when there are Li-ions in standard cylindrical form factors that could be just as easil

Probably a non-user-serviceable Li-ion. I dislike that trend, especially when there are Li-ions in standard cylindrical form factors that could be just as easily changed as AA or AAA. Possible counterpoint: getting a Li-ion 14500 confused with a AA and putting it in an incompatible device is bad.