If you are worried get this:
Nitecore Intellicharge F1 Smart Battery Charger for Li-ion, IMR Batteries
Sorry about the blue text as pasted the name. I have one and the pro being you control the battery which IMHO is the potential issue with any of them. You know the history of the 18650 being used and if there are problems like the battery was overly discharged (the F1 has protection against that) or somehow exposed to whatever just replace the battery.
I like that this nightcore (or 'nightmare', as my phone spell correction keeps auto replacing) is abs and can charge cell phone and internal. . Abs, being very lightweight and fire retardant. . I will need to look into or test this fire claim myself. I am interested in thin, light 18650 flame shielding - from my phone to my 12 hour running headlamps I use daily.
I never went imr as their capacity is so poor. Also think their chief safety selling point is discharge safety and not overcharging safety. . I never will use any light that can go above 350 ma per cell-higher current lights go into the garbage or storage drawer. So, I just use protected name brand Panasonic 3400mah, tested/smart charger that stops at 4.2 volts, and regular dmm volt meter testing off charger. Overcharging is main reason for explosions. . Fake protection circuits too. . Though I plan to build a one handed cell volt tester, since dmm testing takes 3 hands and often daily time constraints means skipping this step.
Also, why is this nightcore marketed as the first outdoor charger? Waterproofing is good, especially where heat dissipation and weight aren't compromised. . My homemade headlamp bezel that secures the reflector is open air, so I get airflow around aluminum reflector, the inside bezel metal, airflow on mcpcb of led. . I do thermal epoxy to waterproof my electrical connections and to keep the reflector and ar glass air tight.... My moto g4 claims a nanotechnology spray to waterproof the circuit boards, rather than trying to waterproof the case.
My other question for previous response from Timothy bill's cat's cccv board suggestion is, where can you get a charging cc/cv board that doubles as a cell charger?
Feel free to dispute me on my imr overcharging conclusion. . I am interested in the truth. And it is in my interest if I am wrong, as this would mean more battery options, even if the capacity doesnt match my typical cc runtime output spec, yet.