Tesiyi were so kind to send me 4pcs 18650 40A battery samples for review and I can use two of them in my Sigelei 100w and another two in my Snow wolf 200w perfectly. Tesiyi Company seemingly sprung up out of nowhere. They said their battery has been highly recognized with its lower internal resistance. 18650 40A battery Its wraps is delicate, it is a flat top battery. Someone believe that these are re-wrapped batteries. My opinion: I think these are factory made batteries, not re-brand second hand crap. Its flat top is a similar to the efest, however its internal resistance is higher than Tesiyi battery. So they are not the same battery. My older Sigelei 100w with this battery It is also suitable for the mechanical. However that leads us to the next thing, it is really a 25A continuous discharge battery and the max continuous discharging current is 40A. I like these batteries a lot and I would recommend them. However just be safe with those super sub ohm builds, use your brain.