The hottest drop-ins you can get for a 3D Mag: 1.) Malkoff Devices Quad-Q5. It needs a minimum 3.8v to run in regulation. 2.) 5x or 4x SSC P4 drop-ins from Elektro Lumens. Sketchy availability, but they can be had. They are usually wired for 4.5v. 3.) 3x K2 TFFC with optics from Terralux. Available at several dealers, including Battery Junction.