I've spoken up about this issue before, and got a bit of flak from it and ended up starting (and being involved in) a bit of a flame war.
So . . . I'll try and be a little more careful in my presentation this time.
Nonetheless . . .
It is my considered opinion that
many people here on CPF drop a
lot of money and go to a lot of trouble in order to be able to use rechargeables in their various lights. And there is often a lot of talk of "guilt free" lumens.
Now, in my estimation, in a large percentage of these cases, the people would have been better off financially if they had just spent all that money on a big ole box of primary cells. It's not always the case, of course, and does depend on your situation, but the point I'm trying to make is just that it seems to be a foregone conclusion for many people that primaries are a waste of money and rechargeables are basically free.
Not true.
There is no such thing as "guilt free lumens" if by that we mean a light that is free to run after an initial expense. Some lights come close, I will admit, but all rechargeable batteries fail, prematurely or not, so at the very least, there is that consideration.
Anyway, what I'm getting at here is the strange mentality that will drop $500 or even $1500 dollars on lots of really cool and amazing lights, but then balk at dropping $100 on batteries. Or the mentality that refrains from running the lights due to the cost of primary cells.
Somehow, it's OK to drop crazy amounts of money on a one-time purchase, but simply "stupid" to spend money running a light like the SF M6 or 12PM or something.
Honestly, I've blown way more money on rechargeable battery packs (either because they failed, or because I accidentally destroyed them or whatever) than I have on primary cells.
And when I buy Duracell or SureFire primaries, I feel fairly confident that they will be ready and able to serve when needed, even 5 or 10 years from now. And I can stash them in various places. I won't go to turn on my light in a power failure and realize that oops it's not charged and not be able to charge it.
Again, it all depends on the individual and his or her useage and ownership patternes. All I'm trying to say is that in some cases, there are people who buy into a rechargeable set up that maybe would have been better off even financially, to have purchased primaries instead.
As for the M6, if you run the MN15, you get 2.5 hours on a set of primaries. That's the way I run my M6, and I love it. See my "X-LOLA" link in my sig-line for more info.