You made the 2D part clear, so that suggests you have one or prefer the 2D to other forms. So the easy and safe way is to stay with AA NiMH. Those batts, however, may add to your costs IF you have buy a light because, as has been suggested, 2, 18650 in a C light can be cheap and avoids the cost of the AA adapter (that can be homemade but is a nuisance project without a decent shop). And lithiums hold a charge a lot longer when not in use, something that may or may not be relevant to your intended use
Right now it seems hard to get 6AA to 2D adapters but it is possible to locate ModaMags 8AA to 2D from the Shoppe and elsewhere. I run a ROP HI in a 2D with this adapter and it works very well.
The other critical component is a reflector. FiveMegas are currently available and I prefer his MOP camless to his others as well as a few other reflectors I've tried.
With the MOP, a ROP HI will easily outreach even the longest reach single SSC led lights in Mag format like the Malkoff (I have one so can readily compare)and even (all of??) the exotic multi-led lights because it has a large and efficient reflector pointing lumens created by 4A of current. Its incan color temp allows better color and depth perception by the human eye, also. It will reach further with a smoothie or VLOP (I have those also) but the pattern out to 200 ft and further is greatly improved with the MOP compared to smoother reflectors. So unless you cruise beanfields for beasts or are trying to spotlight a neighboring building at 400' or more, I'd stick with the MOP.
The UCL lens in mine works fine but then I don't walk around in the rain with it- that might call for a borofloat to stand a better chance of surviving a water hit on hot glass. But even "pyrex" type glasses shatter under rapid temp changes IF their physical expansion/contraction is constrained as it might be in a Mag head.
For AA batteries, stick with "made in Japan" stuff that is correct size. That means Rayovacs, Eneloops and other Sanyo's etc. I've tried the Energizer, match up the positions so it fits drill, and it is NOT a reliable method even when done with the assistance of a digital caliper to confirm measurments and mark cells. It works sometimes but for practical purposes I consider Energizers unusable in a ModaMag 8AA - 2D adapter for a 2D mag, except in a bored tube and you really don't want to waste time on such silliness if you don't have a machine shop. You'll get old fast trying to bore a mag with a brake hone, a device not intended to remove large amounts of metal in a hurry. I use 7 NiMH AAs in mine and made a dummy batt from 1/2" aluminum rod (only because I didn't have any copper rod in my garage -just cut a hunk to length and trimmed one end down to make the equivalent of a + batt terminal, taped the outide, and popped it in the holder in place of the eighth cell.
Haven't bothered with any spring mods or switch fixes, yet, and nothing's melted, yet. But I will probably do both as precautionary improvements. I should note the 2D Mag I'm using has the spring seating at the upper part of the cap on a surface that appears unanodized from the factory.
I've only tried the 3 ROP HI and LO bulb sets I have, but have not encountered any bad bulbs or instaflashes yet out of these 6. Some folks seem to run into these and you might also. I've seen lots of poorly made xenon bulbs offered for sale - for automotive uses poorly made "xenons" out of Asia are ubiquitous, so much so that I source automotive bulbs only from identifiable trusted makers. I've lost count of the number of poor halogens/xenons I've grenaded in vehicles.
So total cost is
Batts $15 approx? depending on source and type
Reflector $25 plus shipping
Batt holder $30 plus shipping
Lens $5 plus shipping
ROP bulbs $10 approx plus shipping
Maybe $90 total if you have the light and buy from as few sources as possible? The wild card for cost is whether you own chargers for anything or need to buy one.
The 2D ROP (any ROP) is an amazing light for the $. If your other stuff is all led's or normal mags using regular or mag-matched xenons, you will probably be surprised by the ROP. But get used to charging cells. Either wiring to charge in the holder or a good 8 AA charger is a help because run times are not huge with this amount of current draw. But charging outside the holder does allow one to inspect cells regularly, not a bad idea when sucking 4A from them. And a very useful safety precaution if you use unprotected 18650s, IMO. And remember the ROP needs open space to cool and don't put it where it can get turned on accidentally. (Another reason why mine is RED)
BTW, my EDC is also a P1D-CE, with the "Nereus Mod" (THANKS, Nereus!) of an SSC with cutdown McR 20S reflector. Much more useful beam and better color balance, though some throw is lost. It makes a better "under the vehicle" inspection light. I've made a few for gifts, also. Not too hard to do if you have careful hands and decent soldering tools but can destroy the light when opening the head if you are clumsy or incautious.
Disclaimer: I'm no flashlight guru as the sig notes. I can do led and bulb swaps, simple electrical calcs, fit parts, assemble boards into lights, etc and that's about it. A lot of my experience with lights comes from upgrading built in or add on driving lights for use on vehicles at speed. So keep that in mind when evaluating the above comments.
Enjoy your ROP
Racer7
