I'm new to Li-ion batteries and couldn't find this answer even after perusing Battery University and this fine site.
I recently purchased a Ultrafire wf-139 charger and one 14500 battery. I understand that the 14500 battery is 3.7V as opposed to an alkaline 1.5V primary. I am using the 14500 in an Ultrafire no-model number aspheric and the difference with the 14500 is remarkable. What I don't understand is why an 18650 battery is also rated at 3.7V. If I use two CR123 primaries, that is the equivalent of 6.0V. I want to use an 18650 in my old Surefire 6Z with a new P60 drop-in and just figured an 18650 would really kick butt, but now I'm not so sure. What advantage would I realize with an 18650 as opposed to two CR 123 primaries? Is it just run time?
You help is appreciated.