Can the ARB-L1-2600 work in all Fenix flashlights?
No, the ARB-L1 model is a battery which will only work in a very small amount of lights. The RC20 is the only currently available flashlight that uses this battery but it is also used in several discontinued lights: RC10, RC15, UC40, UC40UE, UC45, and UC50.
Most current Fenix 18650 flashlight models run on the ARB-L18 series batteries. If you're interested in batteries, learn more about 18650 lithium-ion batteries.