I would love to have a thread from our resident battery expert HKJ where he rates all the 18650 batteries he has used and tested. I would like a thread where he listed them in his order of preference without regard to cost or capacity. Go right down the line from first favorite to least favorite. Then we mortal battery buyers can use his experience to choose which ones we want to buy taking the cost into account. How about it? Are you up to it HKJ?
It is difficult to rank all the batteries, I can try explaining a bit about the 2900/3100 batteries. They are both based on the same cell NCR18650(A) and all has the same discharge properties, except the 3100 has more capacity. With this there is really no reason to buy the 2900 cell or are there, what is the price for 1 Ah? With Redilast 2900 the price is $6.12 and with Redilast 3100 the price is $6.37 for the same Ah, i.e. you get more capacity for the same money with the 2900 and it is only about 10 minute less runtime for a light that can run 3 hours on the 3100 (See summary).
Next is what name to get on the battery? In my opinion there is not that much difference, until now I have seen two batteries that had some issues, but both will be fixed in next batch (According to the manufacturers). When buying a battery I look at the plus pole, where I prefer a button top and the minus pole is best if it has a metal plate. But this is not going to help me if the battery is to long for the light and the shortest battery is the AW with a flat top!
I would also like the protection to be 30% to 50% above rated current (If you uses incan lights you might want it higher), because that gives the best safety.
None of the battery in my summary is a perfect fit (At least not yet), but depending on what parameter you prioritize there are some good candidates in my summary.
After all this, why not use 2900/3100 batteries for everything? The reason is voltage, the 2900/3100 batteries must be discharged down to 2.5 volt for get full capacity, very few single battery lights can do that, they need more voltage. This battery is best for lights with two or more batteries in series.
For single battery lights, you are probably going to find the best battery in the 2400-2600 mAh range (I need to test some more, before I have the final answer to that) or get some 4.3 or 4.35 volt batteries with the problems that gives.
My summary is with information about the different batteries is here