Not sure if this the right place to ask but;
Going to pick up a Malkoff MD2 w/ a M61w to use for a duty light. In the past I've always used primaries but I'm contemplating a single 18650 simply because the MD2 fits it. The pros of this are longer runtimes vs CR123 x2 and lower cost over time. The cons are the initial cost (battery & charger) and improper charging/discharging hazards. Brightness/output should be the same. Do I have it right or no?
The M61 will not remain in regulation for very long on 1 x 18650. It will start out regulated, but after a short time, it will drop off regulation and begin a very long slow taper of brightness reduction, sort of like the old unregulated lights which slowly got dimmer over hours and hours of time.
Other than that, there's no problem with doing it. You just have to be comfortable with the majority of the use being below the regulation limit, and in direct drive.