A quality lithium-ion high drain rechargeable 18650 battery. Firstly, It's a perfect match for most of the vaporizers and e-cigarette MODs. Also, it has a 2600mAh capacity, 3.7 voltage, and 30A continuous discharge current.
In short, Lithium-ion is considered the most promising chemistry of all batteries. Therefore, their manufacturers have a regular cycle of improvements and goals. So as to, reach the right energy density needed for full-adoption seem achievable.
Finally, the 18650 Lithium-ion battery is getting safer every year. Also, cells are getting more sturdy and most people never have problems. However, in some rare circumstances, cells may malfunction. And, this is -mainly- due to mishandling (short-circuiting or puncturing) that causes serious problems, such as fire.
18650 Battery Specifications