The FW3A is a light with e-switch in the tailcap. It’s parasitic drain according to maukka is 28μA (see: TLF/BLF/Lumintop FW3A review (18650, 3x XP-L HI cool white)). Given a 4000mAh battery capacity this means that the parasitic drain will suck the light dry in around 5952 days (roughly 16 years). If you don’t charge your light within 16 years you might run into problems. Otherwise not.