Be careful with Efest batteriesI don't want to get anyone upset or start a argument.
Efest re-wraps other companies batteries which is no big deal, But Efest exaggerates the battery specs.
What I mean by exaggerates, the purple Efest are not a 20A but are a rewrapped Panasonic NCR18650BE that are only rated for 4A max continuous, 6.5A max pulse
I personally wouldn't use a Efest battery, especially for sub-ohm vaping.
This is the company that first did testing on them, I right click and use Google Translate.
Efest Purple IMR 18650-3100 "20A" Akkutest in der Dampfakkus.de AkkuDB
For Google Translate another site click here
Efest sells 4 different purple 18650 batteries.
All are rewraps.
The 30a cells are re wrapped Sony vtc4s.
(Vtc4s weren't made to be sold direct to the public)
I use efest 30a, 35a, and 38a 18650s, but I do so knowing what they are and knowing those are not legit numbers.
I don't push any cell over 20a.