what's the average life span between charges (I understand it depends on usage)?
I vape pretty heavily and with brand new AW ICR123s I can get 12 hours or more froma fresh pair. Even after several cycles they seem to last a good 8 to 10 hours. Of course, YMMV.
I picked up one of these... SlimLine CR123 (red) ...I never get caught without a battery.