I have been recatching the flashlight bugs in recent months, so here are some of my thoughts:Chemistry: I think INR is probably what popular nowadays, and IMR is phrasing out. ICR definitely is old tech and less stable than IMR.I trust the larger producers like Sony(which now is called Murata, Sony no longer makes them) and Samsung, since they need it for their own electronics, has the QC experience in producing in large volume and have a brand name to protect. KeepPower is also pretty good, since they use Murata/Samsung cells to make their own protected cells.For early 2020, here are my go tos:Sony/Murata VTC6 3000mAh, max discharge at 15-30A(w 80deg temp cut)Sony/Murata VTC5A 2600mAh, constant discharge rate at 25ASamsung 20S 2000mAh, CDR 30ASamsung 30Q 3000mAh, CDR 15A
Sometimes it's a problem on smaller 18650 flashlights. Usually it's ok.Depends very much on the flashlight and manufacturer. With many flashlights, you can usually find a reviewer who mentions if protected cells fit or not.