PSA: This is why you should avoid Ultrafire and sketchy Chinese batteries. There's no protection circuit, despite their claim, and their advertised capacity is 9 times what they're capable of. : r/flashlight
A coupled conjugate heat transfer and CFD model for the thermal runaway evolution and jet fire of 18650 lithium-ion battery under thermal abuse - ScienceDirect
Internova 18650 Battery - Lithium Ion Rechargeable Batteries - 2600 mAh 3.7V- with Button Top - Intervine