GottaZoom, thanks for the tip. I'll check out Lowes and HD today or tomorrow. I don't want to buy a whole bunch of them because I'm not sure how the 501B is going to perform yet. The drop-in came in a gifted FrankenL2M running off a single IMR 18350. I've used the new light with an 18650 in it and the drop-in works great, so I'll be interested in how it works with 2 CR123's. I will only buy known name brands, not interested in the cheapest online.
Someone correct me if I’m wrong, but again - if a drop-in runs well and properly at 4.7v-max via a 18650, isn’t it likely that x2 3v CR123 primaries = 6v will kill the circuitry and emitter unless it’s a high range drop in? Or has this already been considered in this thread?
Yes, it will kill the drop-in.
Regarding CR123A, too much credit is given (at least on CPF) to the supposed 10 year shelf-life. A number of people have discovered that unused CR123A cells, even from Surefire, my be dead (or ‘sleeping’ that can somewhat be recovered but still with capacity loss). I would rather depend on 18650s or Eneloops that are maintained (and thus tested) from time to time.
Yes, that is correct. DX has a high range ramping drop-in that E1320 pointed out for me. I’m running it on 2 14500s in a minimag. I believe SolarForce has some but not sure of reliability since I haven’t bought anything except low voltage from them.
In the UF G4 MCU group buy a few people said their light didn’t run with 2*123 but mine is doing it with 3v SureFire primaries and a very impressive draw for an XRE (it is probably my best thrower . . even farther than an XML aspheric though I still need to run them head to head). The pill from that might fit in C8 lights but probably not P60s. 12 to 14 watts gets pretty warm.
Good points! Problem is car lights have gone for months or years without being used/tested. Heat will pull a battery down much faster according to mfgr tables.
To me the best way around is a combination of things . . such as:
- lights that will take more than 1 form of battery (e.g., 2*123 and 18650)
- spare batts rotated in at a different time than the light’s fresh batteries
- EDC and backup lights/batteries I keep in a day bag with other necessities and emergency gear
- a good charging system for draw from the vehicle (and solar also if possible for preppers).
I rotate stored water based on an electronic calendar entry on my phone, so that might be another layer of protection for testing both primaries and rechargeables that are left sitting (especially in a hot car).
If the drop-in is not marked and questionable as to input voltage, I wouldn’t even try running higher than 4.2v in it. It could survive the trial, but then again it might not.
Well thanks to JaffoAZ, mfm and you for pointing this out to me. The WF-501b came with a very cheap drop-in xenon bulb. With my total lack of experience with CR123 (and most things electronic it seems), I assumed I could substitute another drop-in without issue. Now I know I could fry it and I understand what you are saying. The 18350/18650 drop-in has no special markings to indicate it can take a higher voltage, so I'll check with the donor and see if he knows. Otherwise, my son is getting the original light with the bulb. Even with the xenon bulb, it's fairly bright and useful, but it's funny that the batteries will cost more than the flashlight ($3.99 shipped from ebay).
Yeah, those Xenon drop-ins were definitely designed to handle a higher voltage. The one I have is going to be retired now that I’ve got these other torches with way more output and better runtime.
BetweenRides, glad it’s all making some sense. I’m still pretty new to this stuff, so I appreciate the excercise, and glad I could help. Learned some things myself in this thread. 
With that in mind, that xenon bub could eat batteries if it will be used much . . you might want to order something rated up for 8…4v to save on battery replacements if the other one turns out to not be rated higher.
I gave my youngest son one of our old 2D lights when we got his new car . . he didn’t use it once in 3 years (lived out of state) and when I checked the alkys were dead and leaking. Cleaned it up and put it back in with fresh alkys for now - will look for a Christmas deal.
Good point. I might be better off keeping it as an 18650 junker for myself and bringing him a couple of zoomies and my Mini Maglite Pro+ so he can decide which one he wants. He plans on using Eneloops in those. I swore off Alkileaks last time they leaked. Honestly, he's at an age where it doesn't make sense to give him something expensive. It will probably be neglected or ruined in a year. I can always pick up another Sipik clone for $7.
Choice of zoomies would be what I would do in that case . . with our kids some gifts become treasured but nothing works better than having to earn something for it to be valued.
aka battery and parts carrier
oops, sorry! 
so you actually bought that fleabay $4 xenon 501b that I linked in the solarforce thread? :) i mentioned that as a fun host to "park" a spare p60 dropin, but since you got it, does a 18650 fit in there instead of 2xcr123? If you're giving it away, might as well add a UF $6 xre dropin(link), or $6.70 xpg, both of which will take 2xcr123 or 1x18650 if it'll fit. But then again, you'll have spent over $10 for the complete light, whilst you could have just bought the complete xml 501b for $10. I actually wanted an L2m for the car, glad i didn't get it, after the comment above about cr123's not lasting. No need to mess with the sk68 and energizer lithiumAA in there. :)
Well, that may be true of people who carry a flashlight as part of their duty gear, but I use the ccr123a battery because I’m a lazy flashlight user. Lithium rechargeables seem to be to be suck a pain in the rear that I just pony up the cash once every couple of years to buy primaries in bulk to keep the per battery cost reasonable and then just go about my day.
Plus, I can easily carry four spares in my watch pocket with this PowerPax battery Caddy.
I do use Eneloops AA and AAA for some flashlights and all the regular family and kid stuff around the Cone compound, but they are simple to use.
In the end, the choice of battery really depends on whether you are a “hobbyist” or a “pragmatic user”. Nothing wrong with being in either camp.