The IRAY-AC37 BOLT Series Battery Extender threads directly onto the 18500 battery compartment of a BOLT Series, allowing the installation of an 18650 battery which extends battery life by more than 75%. The IRAY-AC37 is compatible with BOLT TL35, TL35V2, TH35C, TH50C, TH50CV2, and TD50L models (not compatible with BOLT SE Series models). The IRAY-AC37 is designed for use with flat-top 18650 batteries only (not compatible with button-top 18650 batteries).