Those are nice dedicated rail mounted lights. Run time does drain out a set of primaries in a relatively short time frame when compared to many of todays designs. Depending on what production vintage you have they can have a slight blue/green tint in the visible spectrum LED. Also the early ones were only 100 lumens while later production are 150 lumens. Not that lumens truly matter IMO especially if you trained MOUT or some form of military combat training. Going active is the last thing you should have on your mind when taking a stroll with a weapon. Which is why having the IR LED in the same focal plane is welcomed. But then you need NODS. I like mine since they are extremely durable and were designed specifically for weapon mounted applications.
Surefire will, without questions asked, repair or replace the KM3 head if yours develops any issue. I've purchased several over the years that had a dim or flickering primary LED and they didn't even balk whether I bought it new or used. Just sent it in and a brandy NEW KM3 showed up on my doorstep.
It will run on a single 3.7 volt cell. The head was not designed for anything above 6 volts. I read a post somewhere a few years back where someone claimed to run one on 3 primaries but I wouldnt take the chance since everything you see says 2 primaries. I've run mine on the newest 16650/ 2500 cells and you get a nice solid 1 hour at full brightness and it will begin tapering off down to somewhere around 50 lumens after almost 3 hours continuous use. Unfortunately that's nothing to brag about. However if extended time night activity is your thing than the more modern version should be in your sights (so to speak) or at least have the MH90 body bored for a 18mm cell and you should be able to improve the performance by at least another 33%.
Another body the KM3 fits is the V2 Vampire. I've never used my V2 for anything other than just sit in the collections box. While on the other hand I have used my M952V on quite a few snoop and poop outings. Go figure? Good luck with your decision and welcome to the forum.
