Hello xdsub.
Before I made the move to 18650 batteries, I also purchased 2 lights that required 2 CR123 primary batteries in each one. Actually, I had never heard of 18650 batteries before joining this forum.
My 1st two LED lights are the original Gladius and a Fenix P3D. I quickly got tired of buying C123 primary (a.k.a. non-rechargeable) batteries. I my case, the Gladius wasn't rated for 3.7v RCR123 batteries.
My very first experience with rechargeable LiOn batteries were ones that were protected and had a 3.0V rating. I did this so that theoretically they would work in flashlights that were only rated for CR123 primaries (3.0vdc).
Note: RCR123 LiOn batteries have several different ranges of voltages. Typically they are 3.7 vdc (4.2v right after removing from the charger).
1) You need to make sure that the charger you are using correctly matches the nominal voltage of the batteries.
2) To a lesser extent the charger should not try to charge the batteries too quickly for their rated capacity.
You really need to be careful with LiOn batteries and their charging/discharging. Especially if the flashlight is multicell (more than 1 battery in series).
My 1st LiOn battery/charger purchase was done with buying a kit. The kit is:
http://www.thomasdistributing.com/s...html?SP_id=&osCsid=a98rm8a91donrsllit8gi3gna7
I haven't had any problems with these 2 kits. I haven't heard/read of any problems either. They aren't the quickest chargers on the market, but that's ok with me. Do not mix these chargers or batteries with other chargers or batteries.
Please realize that these batteries do not have a lot of capacity (compared to RCR3.7v LiOns or primary batteries), but they work well for me. I Purchased 2 sets of these and the 4 batteries are still in use today, over 4 years ago and they get used weekly in the 2 flashlights I described earlier.
DO NOT, I repeat DO NOT use these batteries in Surefire Incandescent lights (see warnings on the page in the link). But for LED lights, I have had no problems.
The other charger that I use for RCR123 3.7v (and 14500 and 18650) batteries is the AW-139. (Search for it, you can find them anywhere). If you purchase one brand new you should be ok. This model went through at least 3 revisions that changed charging voltages that some felt were unsafe. The most recent revision seems to be ok. I would recommend buying only from a reputable dealer (not ebay or amazon) that sells a lot of them so you will less likely to get "old stock" (one of the earlier revisions). I would also suggest to buy "protected" cells. You can read up on what this means. I have had very good luck with the "AW" brand manufacturer of these cells. Again, a search will show suppliers (a few are members of this forum).
My next 3.7v LiOn charger will be one by a company called PILA. It has a very good reputation on this forum. It's relatively expensive, but seems to be worth it.
http://www.pila-usa.com/pilaparts/charger.html
Long since then, for all new purchases, I have moved to AA-based flashlights that accept 14500 batteries since with 14500's they are comparable to RCR123 batteries in performance and are typically smaller diameter (although not always). For my "thrower" lights, a requirement is that they accept 18650 cells, otherwise, they don't make the 1st cut on my roster list.
This should be enough background info to get you going in the right direction. I strongly urge you to use the search function of the forums. There's an entire forum just for batteries and chargers. There is literally hundreds of years of experience, if not thousands, amongst all of the members/posts here. Good luck.
