Built-in heat and fault (short-circuit) protection
Does that mean that they are a protected battery and the chance of them having an issue due to one being lower voltage than the other is minimized?
I am in need of 4 for a camping trip coming up and I can buy Surefire’s local…I want to order some 18650’s so I can run single cells but don’t have the time to get them before we leave so am looking at the CR123A option…just want to be as safe as possible…
thanks
I’ve always mixed and matched different makes, capacities and not had a problem in all my years, I’m now 47, done this with all battery types not just NIMH NICD, but also Lion etc.
tabs
Matched being a very important word.IE same voltage 
CR123 dont have short circuit or overheat protection.
Dont mix CR123 with different voltage, different age or use old CR123. The most nasty accidents happened with these cells!
They often have a PTC and it does work as short circuit and overheat protection.
I agree.
I did not know that. But if that PTC works the same as it does on our "unprotected" LiIon rechargeables, its not advisable to rely on or trigger it.
You are correct, it is only an "emergency stop", not for regular use. There is also differences between brands on how well it works.
Hm, and what does happens when two CR123A’s are being used in series at current too low to be affected by PTC?
Would something bad happen when one cell completely depletes, and due to capacity mismatch, which is always there (even if it’s miniscule) gets reverse charged? :s
Best case: nothing.
Worst case: http://www.candlepowerforums.com/vb/forumdisplay.php?107-Smoke-and-Fire-Hot-Cells-and-Close-Calls-The-dangerous-side-of-batteries
The PTC does not protect against reverse charge.
I have not seen the test procedure for CR123 batteries, but I would expect it to include some reverse charge tests.
But sometimes they do explode when reverse charged, i.e. if you light goes out due to depleted batteries, it is important to turn it off (or remove the batteries).