Do you want to run your existing Surefire tail caps and Surefire or Unity Tactical remote switches with the REIN 3.0? If so, that moment has arrived! The new REIN Legacy light body accepts Surefire tail caps and ALL the existing and corresponding remote switches on the market that work with it. REIN 3.0 runs on 18650 and now can also run on two CR123 batteries. 18650 rechargeable battery provides the best output, by far. However, you can now use 2 CR123A batteries if needed. THIS IS A LIGHT BODY AND 18650 BATTERY COMBO ONLY!