18650 replaces CR123 batteries? They look more like a AA batteries to me.
Did you look at any next to any other items or you just looked at a picture of a single battery and assumed that sense it was about the right shape for a AA that it must be a AA without considering size?
It is the same size as 2 CR123 batteries as I stated.
Confusion with AA batteries comes with the 14500 battery which is the same size and can be substituted in some cases for a AA, but runs 3.7 volts. The 18650 also runs 3.7 volts, but will substitute nicely and run most LED lights better than 2 CR123 batteries.