XTAR 18700 2600mAh
dont fit in all samples of Eagletac T20C2 MkII XM-L U2 because the pin of the tailcap (it's not a bare spring but a gold/brass/silver/aluminum pin!) can be pressed fully down OR NOT. if the tailcap is a perfect assembly of parts (spring, pin, ..), then the pin can be pressed all the way down, and 18700 will fit. otherwise the pin can be depressed only 70% ("bad tailcap") and the tailcap wouldnt close with 18700's. so generally speaking, 18700 fit in the T20C2 MkII, and if there is the pin problem with the tailcap, one has to ask the dealer for ..etc..