No, it wont come with a battery, unless you find a vendor that is selling them as a package deal.
UPDATE to earlier posts: Got my Mutant and was a little shocked at first. The 510 adjustable pin assembly had fallen down into the tube. When I tried to screw it in, it didn't grab the threads until the last couple threads. As such, putting an Atty on top would push it back out.
Looking at the threads closely, they weren't stripped, just really small. So I guess the threading isn't a good match, at least in mine. That said, its nothing a 1-in strip of plumbers tape and a little torque couldnt fix.
Once I fixed that, adjusted the pin down to the battery, and put the magnet pieces in correct position, its hitting hard and great. Love it.
So my critiques are these:
-Piss poor packaging as the tube was just in the mailer. The plastic sleeve was just in the bottom of the bag. (This is on Fasttech, not the mod)
-510 pin needed extra care
-no battery vents
-The depth of the 510 is shallow and non-adjustable. So far, none of my toppers sit flush.
It's a great looking mod and performing well after the tweaks. Plus, its like holding a lead pipe in your hand, so it can help you out in a dark alley.