Holds two CR123'a batteries.  Just load the batteries into the magazine, and slide the magazine into your light.  Takes up the extra space when using CR123a batteries in flashlights that can also use an 18650 battery... no more battery rattle!

Also great to store batteries and have them ready to load into your flashlight... less fumbling in the dark!

RCR123 batteries will not fit (they're slightly too fat), only CR123a batteries. 

Also works with most other flashlight brands!