Felixbelibel Hi,Description on Banggood is bad Not precised unprotected cell I check at Niwalker website ans they say Samsung 40T, so highdrain <20A unprotected cell Technically nitecore, acebeam, imalent and other brand who sell our branded cell with our light are protected and button top And in spec Samsung 40T is 21mm diameter and 700mm length Nitecore is 22mm diameter and 750mm length But they are all in 21700 categorize :( The nitecore cell is just too length for be usable in the niwalker light. For futur buy you must see is the brand sell cell too so Niwalker, lumintop , astrolux and other brand on banggood we don't cell cell with here brand, no astrolux cell for example They are all usable with unprotected cell Sorry for my bad english just say to you only unprotected flat top cell can be good If our 18650 cell work its because is protected and have a length 700mm and not 650mm in relity You can buy Samsung 40t on banggood and try this code for reduction BG1PSS If you have buy the nitecore cell at same order of your Niwalker light try to negociate with banggood to partial refund or discount 40T cell, because the description on the production no say Unprotected cell only. Have a nice day