^^ you can get a pair of 18500's, and a 75mm pvc sleeve to go around them. Then use a 5 cell bulb. That mod gives about 175 lumens while staying with stock reflector and lens.
Or a tad customs G4 setup, which uses a bipin bulb similar to a Magcharger bulb.
Others have used 18650's with some tail cap spring removal then use a TadCustoms or FiveMega bi-pin module and again Magcharger type bulb.
There are other mods that can be done but those are the easiest to do. The G4 setup involves swapping to a metal reflector and glass lens.
Or a tad customs G4 setup, which uses a bipin bulb similar to a Magcharger bulb.
Others have used 18650's with some tail cap spring removal then use a TadCustoms or FiveMega bi-pin module and again Magcharger type bulb.
There are other mods that can be done but those are the easiest to do. The G4 setup involves swapping to a metal reflector and glass lens.