Running 2 18650 in parallel

I would like an expert opinion on what issues i might encounter powering a led or two by using 2 parallel driven 18650 instead of serially. Main concern is safety.

I am not an expert but I would think that the parallel would actually be safer than in a series?

That's my reasoning, but im interested how that 1 battery interact with the other. For example when one of them is going to trip the protection pcb will the other keep preventing that by charging it slightly with few mV? Doing so might be considered usafe or would end up disrupting current flow? Usually battery packs goes 2 serial, 2s2p and so on. I would really like some1 with deep enough technological background to write a pro and con with a nice wrapup in the end.

If i decide to expand... 2S2P might be quite safe for 4 18650, would be much better probably than a 4P setup. Also regulating output is way easier from 8,4V than on 4.2...

The protection circuits rarely trip on low voltage - very few or none of mine do. However, as current usage tends to rise with dropping voltage they all cut out on upper current limit.

If one cell is charging the other, there will not be a voltage issue until both are "below the line".

My take on it.

As long as the two cells are of the same nominal capacity (A few tens of mAh either way will not be a problem) and the same state of charge obviously.

Then there will be no large current flows between the cells which is the only real risk. Small differences will equalise quickly enough. I'd say that parallel cells are a lot safer than series ones as they keep currents seen by each cell to much lower levels. This was less of an issue before Luminus (SST/SST-50 90 360) emitters which like a lot of current. At the three or so amps an XM-L wants, even the crappiest 18650s should be safe enough.

Thanks! It is always you to come to the rescue! :)